Reset more of the state when a mute expires.

This allows the comment box to show up again in a normal state with no 
errors.

src/views/preview/comment/compose-comment.jsx

@@ -59,7 +59,8 @@ class ComposeComment extends React.Component {
     setupMuteExpirationTimeout (muteExpiresAtMs) {
         // Change state when the mute expiration fires if the user is still on the page.
         setTimeout(() => {
-            this.setState({muteExpiresAtMs: 0, muteOpen: false});
+            this.setState(
+                {message: '', muteExpiresAtMs: 0, muteOpen: false, status: ComposeStatus.EDITING, error: null});
         }, muteExpiresAtMs - Date.now());
     }
     handleInput (event) {