message: sized_buffer: use reserve instead of reserve_exact when possible
diff: @@ -17,7 +17,7 @@ impl SizedBuffer {
  if self.inner.len() + amount > self.limit {
  self.inner.reserve_exact(self.limit - self.inner.len());
  } else {
  - self.inner.reserve_exact(amount);
  + self.inner.reserve(amount);
  }
  }
  