If we have nothing to send in the autobatcher, we shouldn't send anyt…

…hing.

Fix #12

src/auto_batcher.rs

@@ -128,6 +128,10 @@ impl AutoBatcher {
     /// batcher.flush(); // .await
     /// ```
     pub async fn flush(&mut self) -> Result<()> {
+        if self.batcher.is_empty() {
+            return Ok(());
+        }
+
         let message = Message::Batch(Batch {
             batch: self.batcher.take(),
             context: self.batcher.context.clone(),

src/batcher.rs

@@ -81,6 +81,10 @@ impl Batcher {
         self.auto_timestamp = false;
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.buf.is_empty()
+    }
+
     /// Push a message into the batcher.
     ///
     /// Returns `Ok(None)` if the message was accepted and is now owned by the