refocus-after-toot (#3537)

app/javascript/mastodon/features/compose/components/compose_form.js

@@ -119,6 +119,8 @@ class ComposeForm extends ImmutablePureComponent {
 
       this.autosuggestTextarea.textarea.setSelectionRange(selectionStart, selectionEnd);
       this.autosuggestTextarea.textarea.focus();
+    } else if(prevProps.is_submitting && !this.props.is_submitting) {
+      this.autosuggestTextarea.textarea.focus();
     }
   }