Ignore button and key events while key-handler is running

Related to issue #253, which originally asked for a non-blocking key-handler.

main.c

@@ -458,6 +458,11 @@ void clear_resize(void)
 	resized = false;
 }
 
+Bool is_input_ev(Display *dpy, XEvent *ev, XPointer arg)
+{
+	return ev->type == ButtonPress || ev->type == KeyPress;
+}
+
 void run_key_handler(const char *key, unsigned int mask)
 {
 	pid_t pid;
@@ -468,6 +473,7 @@ void run_key_handler(const char *key, unsigned int mask)
 	int fcnt = marked ? markcnt : 1;
 	char kstr[32];
 	struct stat *oldst, st;
+	XEvent dump;
 
 	if (keyhandler.f.err != 0) {
 		if (!keyhandler.warned) {
@@ -538,6 +544,9 @@ void run_key_handler(const char *key, unsigned int mask)
 			f++;
 		}
 	}
+	/* drop user input events that occured while running the key handler */
+	while (XCheckIfEvent(win.env.dpy, &dump, is_input_ev, NULL));
+
 end:
 	if (mode == MODE_IMAGE) {
 		if (changed) {