fix(ErrorStatusDisplayItem): disable open in browser button on null URL

Disables the Open in Browser, if the URL is null, as otherwise the app
would crash when trying to open the null URL.

mastodon/src/main/java/org/joinmastodon/android/ui/displayitems/ErrorStatusDisplayItem.java

@@ -4,6 +4,7 @@
 import android.os.Build;
 import android.view.View;
 import android.view.ViewGroup;
+import android.widget.Button;
 
 import org.joinmastodon.android.BuildConfig;
 import org.joinmastodon.android.R;
@@ -32,7 +33,9 @@ public static class Holder extends StatusDisplayItem.Holder<ErrorStatusDisplayIt
 
 		public Holder(Context context, ViewGroup parent) {
 			super(context, R.layout.display_item_error, parent);
-			findViewById(R.id.button_open_browser).setOnClickListener(v -> UiUtils.launchWebBrowser(v.getContext(), item.status.url));
+			Button openInBrowserButton=findViewById(R.id.button_open_browser);
+			openInBrowserButton.setEnabled(item.status.url!=null);
+			openInBrowserButton.setOnClickListener(v -> UiUtils.launchWebBrowser(v.getContext(), item.status.url));
 			findViewById(R.id.button_copy_error_details).setOnClickListener(this::copyErrorDetails);
 		}