Fix unsent toot confirmation dialog not popping up in single column (#13888)

app/javascript/mastodon/features/ui/components/compose_panel.js

 import React from 'react';
+import { connect } from 'react-redux';
+import PropTypes from 'prop-types';
 import SearchContainer from 'mastodon/features/compose/containers/search_container';
 import ComposeFormContainer from 'mastodon/features/compose/containers/compose_form_container';
 import NavigationContainer from 'mastodon/features/compose/containers/navigation_container';
 import LinkFooter from './link_footer';
+import { changeComposing } from 'mastodon/actions/compose';
 
-const ComposePanel = () => (
-  <div className='compose-panel'>
-    <SearchContainer openInRoute />
-    <NavigationContainer />
-    <ComposeFormContainer singleColumn />
-    <LinkFooter withHotkeys />
-  </div>
-);
+export default @connect()
+class ComposePanel extends React.PureComponent {
 
-export default ComposePanel;
+  static propTypes = {
+    dispatch: PropTypes.func.isRequired,
+  };
+
+  onFocus = () => {
+    this.props.dispatch(changeComposing(true));
+  }
+
+  onBlur = () => {
+    this.props.dispatch(changeComposing(false));
+  }
+
+  render() {
+    return (
+      <div className='compose-panel' onFocus={this.onFocus}>
+        <SearchContainer openInRoute />
+        <NavigationContainer onClose={this.onBlur} />
+        <ComposeFormContainer singleColumn />
+        <LinkFooter withHotkeys />
+      </div>
+    );
+  }
+
+}

app/javascript/mastodon/features/ui/index.js

@@ -254,6 +254,7 @@ class UI extends React.PureComponent {
     dispatch(synchronouslySubmitMarkers());
 
     if (isComposing && (hasComposingText || hasMediaAttachments)) {
+      e.preventDefault();
       // Setting returnValue to any string causes confirmation dialog.
       // Many browsers no longer display this text to users,
       // but we set user-friendly message for other browsers, e.g. Edge.