more empty write fixes

src/writebuffer.rs

@@ -44,8 +44,10 @@ impl<'a, E: Endianness> WriteBuffer<'a, E> {
 
     /// Push up to an usize worth of bits
     pub fn push_bits(&mut self, bits: usize, count: usize) {
+        if count > 0 {
             self.0.push_bits(bits, count)
         }
+    }
 
     pub fn reserve(&mut self, length: usize) -> (WriteBuffer<E>, WriteBuffer<E>) {
         let (head, tail) = self.0.reserve(length);