fix: avoid char-boundary panic in NBReader::try_read

Author: SAY-5

src/reader.rs

@@ -203,11 +203,9 @@ impl NBReader {
     pub fn try_read(&mut self) -> Option<char> {
         // discard eventual errors, EOF will be handled in read_until correctly
         let _ = self.read_into_buffer();
-        if !self.buffer.is_empty() {
-            self.buffer.drain(..1).last()
-        } else {
-            None
-        }
+        let first = self.buffer.chars().next()?;
+        self.buffer.drain(..first.len_utf8());
+        Some(first)
     }
 }
 
@@ -459,13 +457,17 @@ mod tests {
     }
 
     #[test]
-    #[should_panic = "is_char_boundary"]
     fn test_try_read_multibyte() {
         let f = io::Cursor::new("\u{c3}");
         let mut r = NBReader::new(f, Options::default());
+        let mut chars = String::new();
         let deadline = time::Instant::now() + time::Duration::from_secs(5);
-        while time::Instant::now() < deadline {
-            let _ = r.try_read();
+        while chars.chars().count() < 2 && time::Instant::now() < deadline {
+            if let Some(c) = r.try_read() {
+                chars.push(c);
+            }
         }
+        assert_eq!(chars, "\u{c3}\u{83}");
+        assert_eq!(None, r.try_read());
     }
 }