don't start a drag event if we have just one tab

apps/lib/katetabbar.cpp

@@ -182,7 +182,7 @@ void KateTabBar::mousePressEvent(QMouseEvent *event)
     }
 
     int tab = tabAt(event->pos());
-    if (event->button() == Qt::LeftButton && tab != -1) {
+    if (event->button() == Qt::LeftButton && tab != -1 && count() > 1) {
         dragStartPos = event->pos();
         auto r = tabRect(tab);
         dragHotspotPos = {dragStartPos.x() - r.x(), dragStartPos.y() - r.y()};