Fix NPE

If `directory == null`, we'll NPE on `directory.mkdir()`.

Author: grantland

Parse/src/main/java/com/parse/ParseKeyValueCache.java

@@ -64,7 +64,7 @@
   }
 
   private static File getKeyValueCacheDir() {
-    if (directory == null || !directory.exists()) {
+    if (directory != null && !directory.exists()) {
       directory.mkdir();
     }
     return directory;