tdf#126808 vcl: fix crash due to leaking the frame's buffer vdev

This vdev is used to do vcl-level double-buffering, which is off by
default, but e.g. listboxes/comboboxes use it to avoid flicker with
Windows GDI.

The root cause was introduced in commit
ea5e83abcfa1406c401b8a1ec91efda65373b74b (tdf#92982 vcl: stop
creating/disposing the paint buffer in PaintHelper, 2015-07-30), which
removed the explicit mpBuffer.disposeAndClear() in the PaintHelper dtor,
but forgot to explicitly dispose it elsewhere.

This is now a much more visible problem since commit
d4714b0fdb81e6e561ae526cc517ecc9a40a603e (tdf#101978 vcl
combobox/listbox floating window: avoid flicker, 2019-06-17) as the
infrastructure is used for all list/comboboxes.

Fix the problem by explicitly disposing the vdev before deleting the
frame data, so the underlying GDI resource is released, even if we have
a reference cycle.

Change-Id: Ia217bbd78780a214308e497044e73e378ee8ecd6
Reviewed-on: https://gerrit.libreoffice.org/77370
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins
(cherry picked from commit e71093c0bc52426647a9d3a41ac0643bbc6cb0c6)
Reviewed-on: https://gerrit.libreoffice.org/77395
Reviewed-by: Xisco Faulí <xiscofauli@libreoffice.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/vcl/source/window/window.cxx b/vcl/source/window/window.cxx
index 8df50b57da1f..f2a42cf8edca 100644
--- a/vcl/source/window/window.cxx
+++ b/vcl/source/window/window.cxx
@@ -557,6 +557,7 @@ void Window::dispose()
         assert (mpWindowImpl->mpFrameData->mnFocusId == nullptr);
         assert (mpWindowImpl->mpFrameData->mnMouseMoveId == nullptr);
 
+        mpWindowImpl->mpFrameData->mpBuffer.disposeAndClear();
         delete mpWindowImpl->mpFrameData;
         mpWindowImpl->mpFrameData = nullptr;
     }