Fix a null object reference crash on Emoji Palette

Do nothing if the current EmojiPageKeyboardView is null.

BUG: 13006906
Change-Id: I169b70122ec939075b5be033953b48762fd528fc

java/src/com/android/inputmethod/keyboard/EmojiPalettesView.java

@@ -724,8 +724,10 @@ public final class EmojiPalettesView extends LinearLayout implements OnTabChange
             // canceled.
             final EmojiPageKeyboardView currentKeyboardView =
                     mActiveKeyboardViews.get(mActivePosition);
+            if (currentKeyboardView != null) {
                 currentKeyboardView.releaseCurrentKey();
             }
+        }
 
         @Override
         public int getCount() {