fix: avoid use null mon when session not active

src/fetch/client.h

@@ -83,7 +83,7 @@ setclient_coordinate_center(Client *c, struct wlr_box geom, int offsetx,
 
 	uint32_t cbw = check_hit_no_border(c) ? c->bw : 0;
 
-	if (!c->no_force_center) {
+	if (!c->no_force_center && m) {
 		tempbox.x = m->w.x + (m->w.width - geom.width) / 2;
 		tempbox.y = m->w.y + (m->w.height - geom.height) / 2;
 	} else {

src/layout/arrange.h

@@ -1,6 +1,10 @@
 void set_size_per(Monitor *m, Client *c) {
 	Client *fc = NULL;
 	bool found = false;
+
+	if (!m || !c)
+		return;
+
 	wl_list_for_each(fc, &clients, link) {
 		if (VISIBLEON(fc, m) && ISTILED(fc) && fc != c) {
 			c->master_mfact_per = fc->master_mfact_per;

src/mango.c

@@ -1353,7 +1353,8 @@ void applyrules(Client *c) {
 		}
 	}
 
-	set_size_per(mon, c);
+	if (mon)
+		set_size_per(mon, c);
 
 	// if no geom rule hit and is normal winodw, use the center pos and record
 	// the hit size