fix: avoid panic when parsing with a multi-byte delimiter

Ini::parse split the value using delimiter + 1, assuming the delimiter
occupies a single byte. With a multi-byte UTF-8 delimiter this offset lands
inside the delimiter character, and slicing the string there panics. Advance
by the delimiter's actual UTF-8 length instead.

src/ini.rs

@@ -1017,7 +1017,14 @@ impl Ini {
                                 current_key = Some(key.clone());
                             }
 
-                            let value = trimmed[delimiter + 1..].trim().to_owned();
+                            // `delimiter` is a byte offset, and the delimiter
+                            // itself may be a multi-byte character, so advance
+                            // by its UTF-8 length rather than assuming one byte.
+                            let delimiter_len = trimmed[delimiter..]
+                                .chars()
+                                .next()
+                                .map_or(1, char::len_utf8);
+                            let value = trimmed[delimiter + delimiter_len..].trim().to_owned();
 
                             valmap.insert(key, Some(value));
                         }