[11840] Fix script command modify_npc_flag

Thanks to faq for pointing.
I checked both udb and ytdb, and they don't use this command yet;
If however you use it already check your scripts. (The toggle/add/remove flag must be set in `data_flags`) Sorry for the inconvenience.
Alos added a forgotten break.

Signed-off-by: Schmoozerd <schmoozerd@scriptdev2.com>

src/game/Map.cpp

@@ -3020,6 +3020,8 @@ void Map::ScriptsProcess()
                     else
                         pBuddy->SetFlag(UNIT_NPC_FLAGS, step.script->npcFlag.flag);
                 }
+
+                break;
             }
             default:
                 sLog.outError("Unknown SCRIPT_COMMAND_ %u called for script id %u.", step.script->command, step.script->id);