Prevent a crash caused by empty emoji

The crash happens because the serialization of recently used emoji uses ; to separate the emojis. One of the ASCII emojis however has a ; in the beginning. When this one is used by the user, it causes an empty string to be returned when deserializing.

This commit prevents the crash, but it does not change the serialization, because this would mess with people's already stored emojis.

We probably need a ticket for 1.0 which makes the serialization more robust.

For now, the offending Emoji has been removed and for the people that used it, there will be a nuclear bomb emoji instead of the empty one.

Closes #1015 (closed)