Add back button to RHS threads from pinned posts (#6306)

webapp/actions/global_actions.jsx

@@ -168,7 +168,8 @@ export function emitPostFocusRightHandSideFromSearch(post, isMentionSearch) {
                 type: ActionTypes.RECEIVED_POST_SELECTED,
                 postId: Utils.getRootId(post),
                 from_search: SearchStore.getSearchTerm(),
-                from_flagged_posts: SearchStore.getIsFlaggedPosts()
+                from_flagged_posts: SearchStore.getIsFlaggedPosts(),
+                from_pinned_posts: SearchStore.getIsPinnedPosts()
             });
 
             AppDispatcher.handleServerAction({

webapp/actions/post_actions.jsx

@@ -142,7 +142,7 @@ export function getFlaggedPosts() {
     );
 }
 
-export function getPinnedPosts(channelId) {
+export function getPinnedPosts(channelId = ChannelStore.getCurrentId()) {
     Client.getPinnedPosts(channelId,
         (data) => {
             AppDispatcher.handleServerAction({