* src/cff/cffdrivr/c (cff_get_ps_name): Avoid unnecessary crash.

The situation can happen if `FT_New_Face` (or one of its siblings) is called
with a negative index to get the number of contained faces, followed
immediately by a call to `FT_Get_Postscript_Name`.  While this is not a valid
use of the FreeType library there is no need for a crash.

Fixes #1219.

src/cff/cffdrivr.c

@@ -634,7 +634,7 @@
         return service->get_ps_font_name( FT_FACE( face ) );
     }
 
-    return (const char*)cff->font_name;
+    return cff ? (const char*)cff->font_name : NULL;
   }