Added missing goto in switch statement.

diff --git a/windows/class.c b/windows/class.c
index ce46c95..aaa6c8f 100644
--- a/windows/class.c
+++ b/windows/class.c
@@ -773,6 +773,7 @@
         case GCW_CBCLSEXTRA:
         case GCW_HMODULE:
             retvalue = (WORD)GetClassLongA( hwnd, offset );
+            goto END;
     }
 
     WARN("Invalid offset %d\n", offset);