bit-sequence: Checked decode

Decode the bytes using checked access. This ensures we don't panic on
missing input.

scale-decode/src/visitor/types/bit_sequence.rs

@@ -46,14 +46,16 @@ impl<'scale> BitSequence<'scale> {
             Ok(bytes_after)
         } else {
             let decoder = decode_using_format_from(self.bytes, self.format)?;
-            Ok(&self.bytes[decoder.encoded_size()..])
+            self.bytes.get(decoder.encoded_size()..).ok_or_else(|| DecodeError::NotEnoughInput)
         }
     }
 
     /// Return a decoder to decode the bits in this bit sequence.
     pub fn decode(&mut self) -> Result<Decoder<'scale>, DecodeError> {
         let decoder = decode_using_format_from(self.bytes, self.format)?;
-        self.bytes_after = Some(&self.bytes[decoder.encoded_size()..]);
+        self.bytes_after = Some(
+            &self.bytes.get(decoder.encoded_size()..).ok_or_else(|| DecodeError::NotEnoughInput)?,
+        );
         Ok(decoder)
     }
 }