validate spelldata.sMissile value in ValidateData

- ensure either sType or SFLAG_RANGED-flag in sUseFlags is set

Source/debug.cpp

@@ -1359,6 +1359,8 @@ void ValidateData()
 				app_fatal("Targeted skill %s (%d) does not have scCurs.", sd.sNameText, i);
 			hasScrollSpell = true;
 		}
+		if (sd.sMissile != 0 && sd.sType == STYPE_NONE && !(sd.sUseFlags & SFLAG_RANGED)) // required by On_SKILLXY, On_SKILLMON, On_SKILLPLR
+			app_fatal("Skill %s (%d) supposed to use a missile, but neither sType nor the SFLAG_RANGED-flag is set.", sd.sNameText, i);
 		//if (!(sd.sUseFlags & SFLAG_DUNGEON) && sd.sType != STYPE_NONE && sd.sType != STYPE_MAGIC && i != SPL_NULL)
 		//	app_fatal("GFX is not loaded in town for skill %s (%d).", sd.sNameText, i); // required by InitPlayerGFX
 	}