Added a missing null-pointer check to the timed player pvp/gvg respawn function (mistake in r12232)

git-svn-id: https://svn.code.sf.net/p/rathena/svn/trunk@12423 54d463be-8e91-2dee-dedb-b68131a5f0ec

src/map/pc.c

@@ -4918,7 +4918,9 @@ void pc_respawn(struct map_session_data* sd, uint8 clrtype)
 static int pc_respawn_timer(int tid,unsigned int tick,int id,int data)
 {
 	struct map_session_data *sd = map_id2sd(id);
-	pc_respawn(sd,0);
+	if( sd != NULL)
+		pc_respawn(sd,0);
+
 	return 0;
 }