fix bug

admin/control/mb_special.php

@@ -137,7 +137,12 @@ class mb_specialControl extends SystemControl
         if($special_id > 0 && !empty($keywords))
         {
             $mod_special = Model('mb_special');
-            $mod_special->editMbSpecial(['keywords' => $keywords,'share_image' =>$cover_img],$special_id);
+            if(!empty($cover_img)) {
+                $mod_special->editMbSpecial(['keywords' => $keywords,'share_image' =>$cover_img],$special_id);
+            }
+            else {
+                $mod_special->editMbSpecial(['keywords' => $keywords],$special_id);
+            }
             echo json_encode(200);
         } else {
             echo json_encode(-1);