Fix first letter in chatbox moving player

Fix part of issue MovingBlocks#2833 (Various isses with movement inputs persisting
through the chatbox) where the first letter typed into an empty chatbox was
causing the player to move.

This was caused by the event falling through to the normal event system,
because a path was not marked with eventHandled = true.

engine/src/main/java/org/terasology/rendering/nui/widgets/UIText.java

@@ -360,6 +360,7 @@ public boolean onKeyEvent(NUIKeyEvent event) {
                     String after = fullText.substring(Math.max(getCursorPosition(), selectionStart));
                     setText(before + event.getKeyCharacter() + after);
                     setCursorPosition(Math.min(getCursorPosition(), selectionStart) + 1);
+                    eventHandled = true;
                 }
             } else {
                 String fullText = text.get();