Fixed possible monster speed underflow when mobs leveling up is enabled (bugreport:2237).

git-svn-id: https://svn.code.sf.net/p/rathena/svn/trunk@15529 54d463be-8e91-2dee-dedb-b68131a5f0ec

src/map/status.c

@@ -1786,7 +1786,7 @@ int status_calc_mob_(struct mob_data* md, bool first)
 		status->max_sp += diff*status->int_;
 		status->hp = status->max_hp;
 		status->sp = status->max_sp;
-		status->speed -= diff;
+		status->speed -= cap_value(diff, 0, status->speed - 10);
 	}