Fix crash with new LookupGammaFontRenderer
Bug #6853934

Change-Id: I15e6ca73bfe00eff1a37c4b9d2f7f709ee018eb6
diff --git a/libs/hwui/GammaFontRenderer.h b/libs/hwui/GammaFontRenderer.h
index 9180778..c4a50be 100644
--- a/libs/hwui/GammaFontRenderer.h
+++ b/libs/hwui/GammaFontRenderer.h
@@ -59,6 +59,7 @@
 
     void clear() {
         delete mRenderer;
+        mRenderer = NULL;
     }
 
     void flush() {