tdf#157613 make sure surface is not a null pointer

Change-Id: I8e3c1be3f05f7ccc1f3ba00093cd71a564e5ae9e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/157848
Reviewed-by: Patrick Luby <plubius@neooffice.org>
Tested-by: Patrick Luby <plubius@neooffice.org>
diff --git a/vcl/skia/osx/gdiimpl.cxx b/vcl/skia/osx/gdiimpl.cxx
index 752208c..c4bd751 100644
--- a/vcl/skia/osx/gdiimpl.cxx
+++ b/vcl/skia/osx/gdiimpl.cxx
@@ -224,6 +224,11 @@ bool AquaSkiaSalGraphicsImpl::drawNativeControl(ControlType nType, ControlPart n
                                                const tools::Rectangle& rControlRegion,
                                                ControlState nState, const ImplControlValue& aValue)
{
    // tdf#157613 make sure surface is not a nullptr
    checkSurface();
    if (!mSurface)
        return false;

    // rControlRegion is not the whole area that the control should be painted to (e.g. highlight
    // around focused lineedit is outside of it). Since we draw to a temporary bitmap, we need tofind out
    // the real size. Using getNativeControlRegion() might seem like the function to call, but we need