Don't rely on having a contact added already

Currently getting the following exception for an empty contact list:

Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0
	at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64)
	at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70)
	at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:248)
	at java.base/java.util.Objects.checkIndex(Objects.java:372)
	at java.base/java.util.ArrayList.get(ArrayList.java:459)
	at org.briarproject.briar.desktop.paul.views.BriarUIStateManagerKt.BriarUIStateManager(BriarUIStateManager.kt:32)
	at org.briarproject.briar.desktop.BriarServiceImpl$login$1$2.invoke(BriarService.kt:103)
	at org.briarproject.briar.desktop.BriarServiceImpl$login$1$2.invoke(BriarService.kt:102)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
	at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:215)
	at org.briarproject.briar.desktop.BriarServiceImpl$login$1.invoke(BriarService.kt:99)
	at org.briarproject.briar.desktop.BriarServiceImpl$login$1.invoke(BriarService.kt:82)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
	at androidx.compose.runtime.RecomposeScopeImpl.compose(RecomposeScopeImpl.kt:140)
	at androidx.compose.runtime.ComposerImpl.recomposeToGroupEnd(Composer.kt:2156)
	at androidx.compose.runtime.ComposerImpl.skipCurrentGroup(Composer.kt:2399)
	at androidx.compose.runtime.ComposerImpl$doCompose$2$5.invoke(Composer.kt:2574)
	at androidx.compose.runtime.ComposerImpl$doCompose$2$5.invoke(Composer.kt:2567)
	at androidx.compose.runtime.SnapshotStateKt.observeDerivedStateRecalculations(SnapshotState.kt:523)
	at androidx.compose.runtime.ComposerImpl.doCompose(Composer.kt:2560)
	at androidx.compose.runtime.ComposerImpl.recompose$runtime(Composer.kt:2536)
	at androidx.compose.runtime.CompositionImpl.recompose(Composition.kt:613)
	at androidx.compose.runtime.Recomposer.performRecompose(Recomposer.kt:763)
	at androidx.compose.runtime.Recomposer.access$performRecompose(Recomposer.kt:102)
	at androidx.compose.runtime.Recomposer$runRecomposeAndApplyChanges$2$2.invoke(Recomposer.kt:446)
	at androidx.compose.runtime.Recomposer$runRecomposeAndApplyChanges$2$2.invoke(Recomposer.kt:415)
	at androidx.compose.runtime.BroadcastFrameClock$FrameAwaiter.resume(BroadcastFrameClock.kt:42)
	at androidx.compose.runtime.BroadcastFrameClock.sendFrame(BroadcastFrameClock.kt:63)
	at androidx.compose.ui.platform.DesktopOwners.onFrame(DesktopOwners.desktop.kt:120)
	at androidx.compose.desktop.ComposeLayer$1.onRender(ComposeLayer.desktop.kt:122)
	at org.jetbrains.skiko.SkiaLayer.update$skiko(SkiaLayer.kt:296)
	at org.jetbrains.skiko.redrawer.LinuxOpenGLRedrawer.update(LinuxOpenGLRedrawer.kt:52)
	at org.jetbrains.skiko.redrawer.LinuxOpenGLRedrawer.access$update(LinuxOpenGLRedrawer.kt:14)
	at org.jetbrains.skiko.redrawer.LinuxOpenGLRedrawer$Companion$frameDispatcher$1.invokeSuspend(LinuxOpenGLRedrawer.kt:75)
	at org.jetbrains.skiko.redrawer.LinuxOpenGLRedrawer$Companion$frameDispatcher$1.invoke(LinuxOpenGLRedrawer.kt)
	at org.jetbrains.skiko.FrameDispatcher$job$1.invokeSuspend(FrameDispatcher.kt:36)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
	at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:313)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)