consistent use of [pop|push]IgnoreDamage

Change-Id: I9a1fccc2cb9f2cd2f336218cf336c358c1a87af1
diff --git a/vcl/unx/gtk/window/gtksalframe.cxx b/vcl/unx/gtk/window/gtksalframe.cxx
index 83526a1..df53136 100644
--- a/vcl/unx/gtk/window/gtksalframe.cxx
+++ b/vcl/unx/gtk/window/gtksalframe.cxx
@@ -3444,7 +3444,7 @@ gboolean GtkSalFrame::signalDraw( GtkWidget*, cairo_t *cr, gpointer frame )

    // FIXME: we quite probably want to stop re-rendering of pieces
    // that we know are just damaged by us and hence already re-rendered
    pThis->m_nDuringRender++;
    pThis->pushIgnoreDamage();

    // FIXME: we need to profile whether re-rendering the entire
    // clip region, and just pushing (with renderArea) smaller pieces
@@ -3460,7 +3460,7 @@ gboolean GtkSalFrame::signalDraw( GtkWidget*, cairo_t *cr, gpointer frame )
        pThis->renderArea( cr, &rect );
    }

    pThis->m_nDuringRender--;
    pThis->popIgnoreDamage();

    cairo_surface_flush(cairo_get_target(cr));