Bug 776369 - Fix NullPointerException. r=bnicholson

mobile/android/base/FontSizePreference.java

@@ -136,12 +136,15 @@ class FontSizePreference extends DialogPreference {
         if (mCurrentOrientation != newConfig.orientation) {
             mCurrentOrientation = newConfig.orientation;
 
+            // mPreviewFontView will be null if the dialog has not yet been shown.
+            if (mPreviewFontView != null) {
                 // Recalculate the mPreviewFontView dimensions since we have new screen dimensions.
                 setPreviewFontViewWidth();
                 mPreviewFontViewHeightSet = false;
                 setFontSizeToMaximum(); // Expects onGlobalLayout() to be called.
             }
         }
+    }
 
     /**
      * Sets the preview font size to the maximum given size.