Fix StickyHeader measuring.

It didn't re-measure when pulling an item from the cache, screwing stuff
up after a phone rotation. Had a workaround for it for specific screens,
but this fixes the problem at the source.

Fixes #8583

src/org/thoughtcrime/securesms/search/SearchFragment.java

@@ -121,16 +121,6 @@ public class SearchFragment extends Fragment implements SearchListAdapter.EventL
     });
   }
 
-  @Override
-  public void onConfigurationChanged(Configuration newConfig) {
-    super.onConfigurationChanged(newConfig);
-
-    if (listDecoration != null) {
-      listDecoration.invalidateLayouts();
-    }
-  }
-
-
   @Override
   public void onConversationClicked(@NonNull ThreadRecord threadRecord) {
     ConversationListActivity conversationList = (ConversationListActivity) getActivity();

src/org/thoughtcrime/securesms/util/StickyHeaderDecoration.java

@@ -76,14 +76,17 @@ public class StickyHeaderDecoration extends RecyclerView.ItemDecoration {
   protected ViewHolder getHeader(RecyclerView parent, StickyHeaderAdapter adapter, int position) {
     final long key = adapter.getHeaderId(position);
 
-    if (headerCache.containsKey(key)) {
+    ViewHolder headerHolder = headerCache.get(key);
-      return headerCache.get(key);
+    if (headerHolder == null) {
-    } else {
+      headerHolder = adapter.onCreateHeaderViewHolder(parent);
-      final ViewHolder holder = adapter.onCreateHeaderViewHolder(parent);
-      final View header = holder.itemView;
 
       //noinspection unchecked
-      adapter.onBindHeaderViewHolder(holder, position);
+      adapter.onBindHeaderViewHolder(headerHolder, position);
+
+      headerCache.put(key, headerHolder);
+    }
+
+    final View header = headerHolder.itemView;
 
     int widthSpec   = View.MeasureSpec.makeMeasureSpec(parent.getWidth(), View.MeasureSpec.EXACTLY);
     int heightSpec  = View.MeasureSpec.makeMeasureSpec(parent.getHeight(), View.MeasureSpec.UNSPECIFIED);
@@ -96,10 +99,7 @@ public class StickyHeaderDecoration extends RecyclerView.ItemDecoration {
     header.measure(childWidth, childHeight);
     header.layout(0, 0, header.getMeasuredWidth(), header.getMeasuredHeight());
 
-      headerCache.put(key, holder);
+    return headerHolder;
-
-      return holder;
-    }
   }
 
   /**
@@ -180,10 +180,6 @@ public class StickyHeaderDecoration extends RecyclerView.ItemDecoration {
         ((LinearLayoutManager)parent.getLayoutManager()).getReverseLayout();
   }
 
-  public void invalidateLayouts() {
-    headerCache.clear();
-  }
-
   /**
    * The adapter to assist the {@link StickyHeaderDecoration} in creating and binding the header views.
    *