Fix memleaks by avoiding _checked variants when discarding the result

Thanks psychon for pointing this out in
i3/i3#2450 (comment)!

src/main.c

@@ -826,7 +826,7 @@ int main(int argc, char *argv[]) {
                       (uint32_t[]){XCB_GX_COPY, ~0, XCB_FILL_STYLE_SOLID, XCB_SUBWINDOW_MODE_INCLUDE_INFERIORS});
 
         xcb_copy_area(conn, root->root, pixmap, gc, 0, 0, 0, 0, width, height);
-        xcb_change_window_attributes_checked(conn, root->root, XCB_CW_BACK_PIXMAP, (uint32_t[]){pixmap});
+        xcb_change_window_attributes(conn, root->root, XCB_CW_BACK_PIXMAP, (uint32_t[]){pixmap});
         xcb_flush(conn);
         xcb_free_gc(conn, gc);
         xcb_free_pixmap(conn, pixmap);

src/x.c

@@ -789,7 +789,7 @@ void x_push_node(Con *con) {
             int width = MAX((int32_t)rect.width, 1);
             int height = MAX((int32_t)rect.height, 1);
 
-            xcb_create_pixmap_checked(conn, win_depth, con->frame_buffer.id, con->frame.id, width, height);
+            xcb_create_pixmap(conn, win_depth, con->frame_buffer.id, con->frame.id, width, height);
             draw_util_surface_init(conn, &(con->frame_buffer), con->frame_buffer.id,
                                    get_visualtype_by_id(get_visualid_by_depth(win_depth)), width, height);