Fix a crash caused by SetupBattleground when m_Map is not created.

src/server/game/Battlegrounds/Battleground.cpp

@@ -437,6 +437,13 @@ inline void Battleground::_ProcessJoin(uint32 diff)
     {
         m_Events |= BG_STARTING_EVENT_1;
 
+        if(!FindBgMap())
+        {
+            sLog->outError("Battleground::_ProcessJoin: map (map id: %u, instance id: %u) is not created!", m_MapId, m_InstanceID);
+            EndNow();
+            return;
+        }
+
         // Setup here, only when at least one player has ported to the map
         if (!SetupBattleground())
         {
@@ -1407,7 +1414,7 @@ bool Battleground::AddObject(uint32 type, uint32 entry, float x, float y, float
     // If the assert is called, means that m_BgObjects must be resized!
     ASSERT(type < m_BgObjects.size());
 
-    Map* map = GetBgMap();
+    Map* map = FindBgMap();
     if (!map)
         return false;
     // Must be created this way, adding to godatamap would add it to the base map of the instance
@@ -1504,7 +1511,7 @@ Creature* Battleground::GetBGCreature(uint32 type)
 
 void Battleground::SpawnBGObject(uint32 type, uint32 respawntime)
 {
-    if (Map* map = GetBgMap())
+    if (Map* map = FindBgMap())
         if (GameObject* obj = map->GetGameObject(m_BgObjects[type]))
         {
             if (respawntime)
@@ -1523,7 +1530,7 @@ Creature* Battleground::AddCreature(uint32 entry, uint32 type, uint32 teamval, f
     // If the assert is called, means that m_BgCreatures must be resized!
     ASSERT(type < m_BgCreatures.size());
 
-    Map* map = GetBgMap();
+    Map* map = FindBgMap();
     if (!map)
         return NULL;