systray: avoid dwm crashing when removing the monitor where the systray is running (hotplugging issues)

dwm.c

@@ -1133,6 +1133,8 @@ cleanupmon(Monitor *mon)
 			XDestroyWindow(dpy, bar->win);
 		}
 		mon->bar = bar->next;
+		if (systray && bar == systray->bar)
+			systray->bar = NULL;
 		free(bar);
 	}
 	free(mon);
@@ -1265,7 +1267,7 @@ configurenotify(XEvent *e)
 		sw = ev->width;
 		sh = ev->height;
 		if (updategeom() || dirty) {
-			drw_resize(drw, sw, bh);
+			drw_resize(drw, sw, sh);
 			updatebars();
 			for (m = mons; m; m = m->next) {
 				#if !FAKEFULLSCREEN_PATCH
@@ -1638,11 +1640,12 @@ drawbars(void)
 void
 drawbarwin(Bar *bar)
 {
-	if (!bar->win || bar->external)
+	if (!bar || !bar->win || bar->external)
 		return;
 	int r, w, total_drawn = 0;
 	int rx, lx, rw, lw; // bar size, split between left and right if a center module is added
 	const BarRule *br;
+	Monitor *lastmon;
 
 	if (bar->borderpx) {
 		XSetForeground(drw->dpy, drw->gc, scheme[bar->borderscheme][ColBorder].pixel);
@@ -1656,13 +1659,16 @@ drawbarwin(Bar *bar)
 	rw = lw = bar->bw - 2 * bar->borderpx;
 	rx = lx = bar->borderpx;
 
+	for (lastmon = mons; lastmon && lastmon->next; lastmon = lastmon->next);
+
 	drw_setscheme(drw, scheme[SchemeNorm]);
 	drw_rect(drw, lx, bar->borderpx, lw, bar->bh - 2 * bar->borderpx, 1, 1);
 	for (r = 0; r < LENGTH(barrules); r++) {
 		br = &barrules[r];
 		if (br->bar != bar->idx || !br->widthfunc || (br->monitor == 'A' && bar->mon != selmon))
 			continue;
-		if (br->monitor != 'A' && br->monitor != -1 && br->monitor != bar->mon->index)
+		if (br->monitor != 'A' && br->monitor != -1 && br->monitor != bar->mon->index &&
+				(br->drawfunc != draw_systray || (lastmon->index >= br->monitor && bar->mon->index == 0))) // hack: draw systray on first monitor if the designated one is not available
 			continue;
 		drw_setscheme(drw, scheme[SchemeNorm]);
 		warg.w = (br->alignment < BAR_ALIGN_RIGHT_LEFT ? lw : rw);