[android] Show (tinted) security icon when warning about saving attachments

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageActivity.java

@@ -11,6 +11,8 @@ import android.support.annotation.Nullable;
 import android.support.annotation.RequiresApi;
 import android.support.design.widget.AppBarLayout;
 import android.support.design.widget.Snackbar;
+import android.support.v4.content.ContextCompat;
+import android.support.v4.graphics.drawable.DrawableCompat;
 import android.support.v7.app.AlertDialog.Builder;
 import android.support.v7.widget.Toolbar;
 import android.transition.Fade;
@@ -285,7 +287,10 @@ public class ImageActivity extends BriarActivity
 		Builder builder = new Builder(this, R.style.BriarDialogTheme);
 		builder.setTitle(getString(R.string.dialog_title_save_image));
 		builder.setMessage(getString(R.string.dialog_message_save_image));
-		builder.setIcon(R.drawable.emoji_google_1f6af);
+		Drawable icon = ContextCompat.getDrawable(this, R.drawable.ic_security);
+		DrawableCompat.setTint(requireNonNull(icon),
+				ContextCompat.getColor(this, R.color.color_primary));
+		builder.setIcon(icon);
 		builder.setPositiveButton(R.string.save_image, okListener);
 		builder.setNegativeButton(R.string.cancel, null);
 		builder.show();

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageViewModel.java

@@ -82,7 +82,7 @@ public class ImageViewModel extends AndroidViewModel {
 	@UiThread
 	void saveImage(AttachmentItem attachment, @Nullable Uri uri) {
 		if (uri == null) {
-			saveState.setValue(true);
+			saveState.setValue(false);
 		} else {
 			saveImage(attachment, () -> getOutputStream(uri), null);
 		}

briar-android/src/main/res/drawable/ic_security.xml

+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0">
+    <path
+        android:fillColor="#FF000000"
+        android:pathData="M12,1L3,5v6c0,5.55 3.84,10.74 9,12 5.16,-1.26 9,-6.45 9,-12L21,5l-9,-4zM12,11.99h7c-0.53,4.12 -3.28,7.79 -7,8.94L12,12L5,12L5,6.3l7,-3.11v8.8z"/>
+</vector>