Bug 1397238 - Reset the mIsSimpleFamily flag whenever a face is added to a font family, to ensure we will re-check the available faces before making assumptions about face indexes in FindAllFontsForStyle. r=heycam

gfx/thebes/gfxFontEntry.h

@@ -646,6 +646,8 @@ public:
         }
         aFontEntry->mSkipDefaultFeatureSpaceCheck = mSkipDefaultFeatureSpaceCheck;
         mAvailableFonts.AppendElement(aFontEntry);
+        mIsSimpleFamily = false; // CheckForSimpleFamily may set this later,
+                                 // but at this point we're not sure
     }
 
     // note that the styles for this family have been added