widl: Store the interface id in _StubMsg.MaxCount for iid_is pointers.

tools/widl/typegen.c

@@ -1956,6 +1956,9 @@ void write_remoting_arguments(FILE *file, int indent, const func_t *func,
             }
             else
             {
+                const var_t *iid;
+                if ((iid = get_attrp( var->attrs, ATTR_IIDIS )))
+                    print_file( file, indent, "_StubMsg.MaxCount = (unsigned long)%s;\n", iid->name );
                 print_phase_function(file, indent, "Pointer", phase, var->name, *type_offset);
             }
         }