Codechange: rename str_validate to StrMakeValid(InPlace) (#9304)

This to be more explicit the function changes the value, and not
returns yes/no.

src/saveload/oldloader.cpp

@@ -234,7 +234,7 @@ static inline bool CheckOldSavegameType(FILE *f, char *temp, const char *last, u
 
 	bool ret = VerifyOldNameChecksum(temp, len);
 	temp[len - 2] = '\0'; // name is null-terminated in savegame, but it's better to be sure
-	str_validate(temp, last);
+	StrMakeValidInPlace(temp, last);
 
 	return ret;
 }