Do not scroll timelines when *closing* media modals

Media modals push an history state so that pressing back on mobile closes them.
We made sure to not scroll when opening them, but not when *closing* them,
which caused some issues in rare cases.

app/javascript/flavours/glitch/features/followers/index.js

@@ -57,6 +57,7 @@ export default class Followers extends ImmutablePureComponent {
   }
 
   shouldUpdateScroll = (prevRouterProps, { location }) => {
+    if ((((prevRouterProps || {}).location || {}).state || {}).mastodonModalOpen) return false;
     return !(location.state && location.state.mastodonModalOpen);
   }