Re-add NULL FontMgr::Factory hadnling code removed in r12217.


git-svn-id: http://skia.googlecode.com/svn/trunk/src@12218 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/core/SkFontHost.cpp b/core/SkFontHost.cpp
index ab32dfc..c09739d 100644
--- a/core/SkFontHost.cpp
+++ b/core/SkFontHost.cpp
@@ -193,6 +193,10 @@
 
 void set_up_default(SkFontMgr** singleton) {
   *singleton = SkFontMgr::Factory();
+  // we never want to return NULL
+  if (NULL == *singleton) {
+      *singleton = SkNEW(SkEmptyFontMgr);
+  }
 }
 
 SkFontMgr* SkFontMgr::RefDefault() {