Update the composer height on redraw

For some reason, the text editor isn't being retained across route
changes, and it loses its height style. This reapplies it on every
redraw.

js/forum/src/components/Composer.js

@@ -88,6 +88,8 @@ class Composer extends Component {
   }
 
   config(isInitialized, context) {
+    this.updateHeight();
+
     if (isInitialized) return;
 
     // Since this component is a part of the global UI that persists between