[Glitch] Fix “Back” button sometimes redirecting out of Mastodon

Port a442a1d1c6 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/components/column_back_button.jsx

@@ -20,9 +20,7 @@ export default class ColumnBackButton extends PureComponent {
   handleClick = () => {
     const { router } = this.context;
 
-    // Check if there is a previous page in the app to go back to per https://stackoverflow.com/a/70532858/9703201
-    // When upgrading to V6, check `location.key !== 'default'` instead per https://github.com/remix-run/history/blob/main/docs/api-reference.md#location
-    if (router.route.location.key) {
+    if (router.history.location?.state?.fromMastodon) {
       router.history.goBack();
     } else {
       router.history.push('/');