Fix Coverity CID 468122

Missing break statement in a switch intoduced by commit
54acca4

The results of this are benign, as the extra code which is run is
unlikely to do anything.

Author: matt335672

xrdp/xrdp_wm.c

@@ -2148,6 +2148,7 @@ callback(intptr_t id, int msg, intptr_t param1, intptr_t param2,
             xrdp_mm_suppress_output(wm->mm, param1,
                                     LOWORD(param2), HIWORD(param2),
                                     LOWORD(param3), HIWORD(param3));
+            break;
         case 0x555a:
             // "yeah, up_and_running"
             xrdp_mm_up_and_running(wm->mm);