[Glitch] fix: initial state of PrivacyDropdown is should not be null

Port bebe8ec887 to glitch-soc

app/javascript/flavours/glitch/features/composer/options/dropdown/index.js

@@ -131,7 +131,7 @@ export default class ComposerOptionsDropdown extends React.PureComponent {
     this.state = {
       needsModalUpdate: false,
       open: false,
-      placement: null,
+      placement: 'bottom',
     };
   }