mshtml: Mark fall-through in switch statement

[Andrew Talbot]

Changelog:
    mshtml: Mark fall-through in switch statement.

diff --git a/dlls/mshtml/htmlevent.c b/dlls/mshtml/htmlevent.c
index 93a5367..2b9e62e 100644
--- a/dlls/mshtml/htmlevent.c
+++ b/dlls/mshtml/htmlevent.c
@@ -1229,6 +1229,7 @@ HRESULT set_event_handler(event_target_t **event_target, nsIDOMNode *nsnode, HTM
 
     default:
         FIXME("not supported vt=%d\n", V_VT(var));
+        /* fall through */
     case VT_EMPTY:
         return E_NOTIMPL;
     }