add some error check and return.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@4912 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/Console/GraphicsConsoleDxe/GraphicsConsole.c

@@ -424,6 +424,9 @@ GraphicsConsoleControllerDriverStart (
           goto Error;
         }
       }
+    } else {
+      Status = EFI_UNSUPPORTED;
+      goto Error;
     }
   }