Add an icon for DiffWidget

To be consistent with other tabs

apps/lib/katemainwindow.cpp

@@ -1332,6 +1332,8 @@ void KateMainWindow::showDiff(const QByteArray &wordDiff, const DiffParams &para
         else
             w->setWindowTitle(i18n("Diff %1..%2", Utils::fileNameFromPath(params.srcFile), Utils::fileNameFromPath(params.destFile)));
     }
+
+    w->setWindowIcon(QIcon::fromTheme(QStringLiteral("text-x-patch")));
     addWidget(w);
     w->openDiff(wordDiff);
 }

apps/lib/katetabbar.cpp

@@ -482,6 +482,7 @@ QVector<KTextEditor::Document *> KateTabBar::documentList() const
 void KateTabBar::setCurrentWidget(QWidget *widget)
 {
     int idx = insertTab(-1, widget->windowTitle());
+    setTabIcon(idx, widget->windowIcon());
     setTabData(idx, QVariant::fromValue(widget));
     setCurrentIndex(idx);
 }