fdo#56970 Fixed insert new sheet button for different directionality

Fixed position of insert new sheet button (+) when using a sheet with
a different directionality than that of the interface.

Change-Id: Ifc7020c4eb7a1686c23b4d827c47494b88a236b5
Reviewed-on: https://gerrit.libreoffice.org/1385Tested-by: Lior Kaplan <kaplanlior@gmail.com>
Reviewed-by: Eike Rathke <erack@redhat.com>

svtools/source/control/tabbar.cxx

@@ -1760,8 +1760,12 @@ Rectangle TabBar::ImplGetInsertTabRect(ImplTabBarItem* pItem) const
     if (mbHasInsertTab && pItem)
     {
         Rectangle aInsTabRect = pItem->maRect;
-        aInsTabRect.setX(
-            aInsTabRect.getX() + aInsTabRect.getWidth() - TABBAR_OFFSET_X - TABBAR_OFFSET_X2);
+        if ( !mbMirrored )
+            aInsTabRect.setX(
+                aInsTabRect.getX() + aInsTabRect.getWidth() - TABBAR_OFFSET_X - TABBAR_OFFSET_X2);
+        else
+            aInsTabRect.setX(
+                aInsTabRect.getX() - 3*TABBAR_OFFSET_X - TABBAR_OFFSET_X2);
         aInsTabRect.setWidth(32);
         return aInsTabRect;
     }