hide content warning button when there is no content (#4518)

I encountered [this weird
post](https://akko.wtf/notice/Aiz78vrg9jBNHJrvIO) today that had a
content warning button but no content.

<img
src="https://github.com/tuskyapp/Tusky/assets/10157047/975090e1-7552-4750-97b4-1917b06aeb60"
width="320"/>

This change will match Mastodon behavior and hide the button when there
is no content to reveal.

We probably did not encounter this bug earlier because Mastodon moves
the CW to the content when the content is empty, but apparently not for
federated posts.

app/src/main/java/com/keylesspalace/tusky/adapter/StatusBaseViewHolder.java

@@ -235,9 +235,14 @@ protected void setSpoilerAndContent(@NonNull StatusViewData.Concrete status,
             );
             contentWarningDescription.setText(emojiSpoiler);
             contentWarningDescription.setVisibility(View.VISIBLE);
-            contentWarningButton.setVisibility(View.VISIBLE);
-            setContentWarningButtonText(expanded);
-            contentWarningButton.setOnClickListener(view -> toggleExpandedState(true, !expanded, status, statusDisplayOptions, listener));
+            boolean hasContent = !TextUtils.isEmpty(status.getContent());
+            if (hasContent) {
+                contentWarningButton.setVisibility(View.VISIBLE);
+                setContentWarningButtonText(expanded);
+                contentWarningButton.setOnClickListener(view -> toggleExpandedState(true, !expanded, status, statusDisplayOptions, listener));
+            } else {
+                contentWarningButton.setVisibility(View.GONE);
+            }
             this.setTextVisible(true, expanded, status, statusDisplayOptions, listener);
         } else {
             contentWarningDescription.setVisibility(View.GONE);