Fix NPE

Change-Id: I35efd1d6c8c2b48d93675d014d5c7aef7d12ed58
diff --git a/java/src/com/android/inputmethod/keyboard/PointerTracker.java b/java/src/com/android/inputmethod/keyboard/PointerTracker.java
index 397ac7e..0a727ad 100644
--- a/java/src/com/android/inputmethod/keyboard/PointerTracker.java
+++ b/java/src/com/android/inputmethod/keyboard/PointerTracker.java
@@ -615,7 +615,7 @@
     // The modifier key, such as shift key, should not show its key preview.
     private boolean isKeyPreviewNotRequired(int keyIndex) {
         final Key key = getKey(keyIndex);
-        if (!key.mEnabled)
+        if (key == null || !key.mEnabled)
             return true;
         // Such as spacebar sliding language switch.
         if (mKeyboard.needSpacebarPreview(keyIndex))