add panics section to digest_pad docs

Author: newpavlov

block-buffer/src/lib.rs

@@ -256,13 +256,19 @@ where
     /// Compress remaining data after padding it with `delim`, zeros and
     /// the `suffix` bytes. If there is not enough unused space, `compress`
     /// will be called twice.
+    ///
+    /// # Panics
+    /// If suffix length is bigger than block size.
     #[inline(always)]
     pub fn digest_pad(
         &mut self,
         delim: u8,
         suffix: &[u8],
         mut compress: impl FnMut(&Block<BlockSize>),
     ) {
+        if suffix.len() > BlockSize::USIZE {
+            panic!("suffix is too long");
+        }
         let pos = self.get_pos();
         self.buffer[pos] = delim;
         for b in &mut self.buffer[pos + 1..] {