st/mesa: fix pipe_query_result result initializer

Fixes MSVC build error.

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>

src/mesa/state_tracker/st_cb_perfmon.c

@@ -266,7 +266,7 @@ st_GetPerfMonitorResult(struct gl_context *ctx,
 
    /* Read query results for each active counter. */
    LIST_FOR_EACH_ENTRY(cntr, &stm->active_counters, list) {
-      union pipe_query_result result = {};
+      union pipe_query_result result = { 0 };
       int gid, cid;
       GLenum type;