Fix conversion of empty vectors to Bytes

Closes #340

src/bytes.rs

@@ -709,6 +709,13 @@ impl From<&'static str> for Bytes {
 
 impl From<Vec<u8>> for Bytes {
     fn from(vec: Vec<u8>) -> Bytes {
+        // into_boxed_slice doesn't return a heap allocation for empty vectors,
+        // so the pointer isn't aligned enough for the KIND_VEC stashing to
+        // work.
+        if vec.is_empty() {
+            return Bytes::new();
+        }
+
         let slice = vec.into_boxed_slice();
         let len = slice.len();
         let ptr = slice.as_ptr();