bg_join - battleground doc update (#5385)

* Added more information in the doc about waitingroom2bg_single and bg_join commands
* Added MF_BATTLEGROUND mapflag check in waitingroom2bg_single and bg_join to prevent the player to join a bg when the battle map is not a battleground map

doc/script_commands.txt

@@ -9392,6 +9392,7 @@ QMARK_PURPLE - Purple Marker
 Adds the first waiting player from the chat room of the given NPC to an existing battleground group.
 The player will also be warped to the default spawn point of the battle group or to the specified coordinates
 <x> and <y> on the given <map>.
+Note: The map need the mapflag MF_BATTLEGROUND otherwise the player is removed from the Battleground team.
 
 ---------------------------------------
 
@@ -9437,6 +9438,7 @@ Returns battle group ID on success. Returns 0 on failure.
 
 Adds an attached player or <char id> if specified to an existing battleground group. The player will also be warped
 to the default spawn point of the battle group or to the specified coordinates <x> and <y> on the given <map>.
+Note: The map need the mapflag MF_BATTLEGROUND otherwise the player is removed from the Battleground team.
 
 Returns true on success. Returns false on failure.
 
@@ -9566,8 +9568,8 @@ Example:
 Retrieves data related to given Battle Group. Type can be one of the following:
 
 	0 - Amount of players currently belonging to the group.
-	1 - Store GID of players in <Battle Group> in a temporary global array $@arenamembers
-		and returns amount of players currently belonging to the group.
+	1 - Store GID of players in <Battle Group> in a temporary global array $@arenamembers,
+		stores and also returns the amount of players currently belonging to the group in $@arenamemberscount.
 
 ---------------------------------------
 

src/map/script.cpp

@@ -19970,6 +19970,11 @@ BUILDIN_FUNC(waitingroom2bg_single)
 		x = bg->cemetery.x;
 		y = bg->cemetery.y;
 	}
+	if (!map_getmapflag(map_mapindex2mapid(mapindex), MF_BATTLEGROUND)) {
+		ShowWarning("buildin_waitingroom2bg_single: Map %s requires the mapflag MF_BATTLEGROUND.\n", mapindex_id2name(mapindex));
+		script_pushint(st, false);
+		return SCRIPT_CMD_FAILURE;
+	}
 
 	nd = npc_name2id(script_getstr(st,6));
 
@@ -20055,6 +20060,11 @@ BUILDIN_FUNC(bg_join) {
 		script_pushint(st, false);
 		return SCRIPT_CMD_FAILURE;
 	}
+	if (!map_getmapflag(map_mapindex2mapid(mapindex), MF_BATTLEGROUND)) {
+		ShowWarning("buildin_bg_join: Map %s requires the mapflag MF_BATTLEGROUND.\n", mapindex_id2name(mapindex));
+		script_pushint(st, false);
+		return SCRIPT_CMD_FAILURE;
+	}
 
 	if (bg_team_join(bg_id, sd, false) && pc_setpos(sd, mapindex, x, y, CLR_TELEPORT) == SETPOS_OK)
 	{