Fixes a map-server crash when using @showmobs (#2997)

src/map/atcommand.cpp

@@ -7346,7 +7346,7 @@ ACMD_FUNC(showmobs)
 
 	if((mob_id = atoi(mob_name)) == 0)
 		mob_id = mobdb_searchname(mob_name);
-	if(mob_id > 0 && mobdb_checkid(mob_id) == 0){
+	if(mobdb_checkid(mob_id) == 0){
 		snprintf(atcmd_output, sizeof atcmd_output, msg_txt(sd,1250),mob_name); // Invalid mob id %s!
 		clif_displaymessage(fd, atcmd_output);
 		return 0;