always apply a minimum size of 1x1

Resizing with the mouse can make the size negative, which makes dwl
crash, and the minimum is 1 because 0 makes some X11 clients crash.

dwl.c

@@ -377,6 +377,7 @@ static void zoom(const Arg *arg);
 static pid_t child_pid = -1;
 static int locked;
 static void *exclusive_focus;
+static Client *focused_client;
 static struct wl_display *dpy;
 static struct wl_event_loop *event_loop;
 static struct wlr_backend *backend;
@@ -487,6 +488,10 @@ static struct wlr_xwayland *xwayland;
 void
 applybounds(Client *c, struct wlr_box *bbox)
 {
+	/* set minimum client size to 1 */
+	c->geom.width = MAX(1 + 2 * (int)c->bw, c->geom.width);
+	c->geom.height = MAX(1 + 2 * (int)c->bw, c->geom.height);
+
 	if (!c->isfullscreen) {
 		struct wlr_box min = {0}, max = {0};
 		client_get_size_hints(c, &max, &min);
@@ -1523,6 +1528,9 @@ focusclient(Client *c, int lift)
 			wlr_xdg_popup_destroy(popup);
 	}
 
+	if (old_c && old_c == exclusive_focus && client_wants_focus(old_c))
+		exclusive_focus = NULL;
+
 	/* Put the new client atop the focus stack and select its monitor */
 	if (c && !client_is_unmanaged(c)) {
 		wl_list_remove(&c->flink);
@@ -1536,24 +1544,23 @@ focusclient(Client *c, int lift)
 			client_set_border_color(c, focuscolor);
 	}
 
-	/* Deactivate old client if focus is changing */
-	if (old && (!c || client_surface(c) != old)) {
 	/* If an overlay is focused, don't focus or activate the client,
 	 * but only update its position in fstack to render its border with focuscolor
 	 * and focus it after the overlay is closed. */
-		if (old_client_type == LayerShell && wlr_scene_node_coords(
+	if (old && (!c || client_surface(c) != old)
+			&& old_client_type == LayerShell && wlr_scene_node_coords(
 				&old_l->scene->node, &unused_lx, &unused_ly)
 			&& old_l->layer_surface->current.layer >= ZWLR_LAYER_SHELL_V1_LAYER_TOP
-				&& old_l->layer_surface->current.keyboard_interactive == ZWLR_LAYER_SURFACE_V1_KEYBOARD_INTERACTIVITY_EXCLUSIVE) {
+			&& old_l->layer_surface->current.keyboard_interactive == ZWLR_LAYER_SURFACE_V1_KEYBOARD_INTERACTIVITY_EXCLUSIVE)
 		return;
-		} else if (old_c && old_c == exclusive_focus && client_wants_focus(old_c)) {
-			return;
-		} else if (old_c && !client_is_unmanaged(old_c)) {
-			if (c && !client_is_unmanaged(c))
-				client_set_border_color(old_c, bordercolor);
 
-			client_activate_surface(old, 0);
-		}
+	if (focused_client && focused_client != c && !(c && client_is_unmanaged(c))) {
+		struct wlr_surface *s = client_surface(focused_client);
+		if (c)
+			client_set_border_color(focused_client, bordercolor);
+		if (s && s->mapped)
+			client_activate_surface(s, 0);
+		focused_client = NULL;
 	}
 	printstatus();
 
@@ -1574,6 +1581,9 @@ focusclient(Client *c, int lift)
 
 	/* Activate the new client */
 	client_activate_surface(client_surface(c), 1);
+
+	if (!client_is_unmanaged(c))
+		focused_client = c;
 }
 
 void
@@ -2980,6 +2990,8 @@ unmapnotify(struct wl_listener *listener, void *data)
 		cursor_mode = CurNormal;
 		grabc = NULL;
 	}
+	if (c == focused_client)
+		focused_client = NULL;
 
 	if (client_is_unmanaged(c)) {
 		if (c == exclusive_focus) {