added missing extern keyword for ms_RoomId in mserv.h (the definition is...

added missing extern keyword for ms_RoomId in mserv.h (the definition is already in the .c file in this case)

(cherry picked from commit 064f4bcf349e9600552a0b99bd0fbfb3cbcf0958)

src/mserv.h

@@ -68,7 +68,7 @@ extern consvar_t cv_masterserver, cv_servername;
 // < 0 to not connect (usually -1) (offline mode)
 // == 0 to show all rooms, not a valid hosting room
 // anything else is whatever room the MS assigns to that number (online mode)
-INT16 ms_RoomId;
+extern INT16 ms_RoomId;
 
 const char *GetMasterServerPort(void);
 const char *GetMasterServerIP(void);