clipmenud: Prevent infinite loop in signal handler

When handling an enable/disable signal, clipmenud could enter an
infinite loop if another X event was already in the queue. The function
to get the server time would repeatedly read and put back the same event
at the head of the queue (er, whoops!).

Instead use XIfEvent, which doesn't bodge the event queue.

Fixes #255.

Author: cdown

src/clipmenud.c

@@ -64,23 +64,22 @@ static void free_clip_text(struct clip_text *ct) {
     ct->source = CLIP_TEXT_SOURCE_INVALID;
 }
 
+// cppcheck-suppress [constParameterCallback,unmatchedSuppression]
+static Bool is_timestamp_event(Display *display _unused_, XEvent *event,
+                               XPointer arg) {
+    return event->type == PropertyNotify &&
+           event->xproperty.atom == *(Atom *)arg;
+}
+
 /**
  * Get the current X server time by triggering a PropertyNotify.
  */
 static Time get_current_server_time(void) {
     XEvent ev;
     XChangeProperty(dpy, win, timestamp_atom, XA_INTEGER, 32, PropModeReplace,
                     NULL, 0);
-    XSync(dpy, False);
-
-    while (1) {
-        XNextEvent(dpy, &ev);
-        if (ev.type == PropertyNotify && ev.xproperty.atom == timestamp_atom) {
-            XDeleteProperty(dpy, win, timestamp_atom);
-            return ev.xproperty.time;
-        }
-        XPutBackEvent(dpy, &ev);
-    }
+    XIfEvent(dpy, &ev, is_timestamp_event, (XPointer)&timestamp_atom);
+    return ev.xproperty.time;
 }
 
 /**