Fix NPE when context.getFilesDir() returns null.

Bug: 16416948
Change-Id: I0fac5ab26d6efbadbd688d033a79f6705e0161a5

java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java

@@ -138,6 +138,7 @@ public class PersonalizationHelper {
             final File filesDir = context.getFilesDir();
             if (filesDir == null) {
                 Log.e(TAG, "context.getFilesDir() returned null.");
+                return;
             }
             if (!FileUtils.deleteFilteredFiles(filesDir, new DictFilter(dictNamePrefix))) {
                 Log.e(TAG, "Cannot remove all existing dictionary files. filesDir: "