Fix off-by-one/buffer over-read error in StrMakeValid

See: https://github.com/OpenTTD/OpenTTD/issues/11644

src/ini_load.cpp

@@ -290,7 +290,7 @@ void IniLoadFile::LoadFromDisk(const std::string &filename, Subdirectory subdir,
 			if (!quoted && e == t) {
 				item.value.reset();
 			} else {
-				item.value = StrMakeValid(std::string(t));
+				item.value = StrMakeValid(std::string_view(t));
 			}
 		} else {
 			/* it's an orphan item */

src/string.cpp

@@ -268,7 +268,7 @@ static void StrMakeValid(T &dst, const char *str, const char *last, StringValida
 		 * would also reach the "last" byte of the string and a normal '\0'
 		 * termination will be placed after it.
 		 */
-		if (len == 0 || str + len > last || len != Utf8Decode(&c, str)) {
+		if (len == 0 || str + len > last + 1 || len != Utf8Decode(&c, str)) {
 			/* Maybe the next byte is still a valid character? */
 			str++;
 			continue;
@@ -341,7 +341,7 @@ void StrMakeValidInPlace(char *str, StringValidationSettings settings)
 std::string StrMakeValid(std::string_view str, StringValidationSettings settings)
 {
 	auto buf = str.data();
-	auto last = buf + str.size();
+	auto last = buf + str.size() - 1;
 
 	std::ostringstream dst;
 	std::ostreambuf_iterator<char> dst_iter(dst);