Make findChild more robust in the face of disposed windows

<https://ci.libreoffice.org/job/lo_ubsan/1815/> had once failed
UITest_sw_styleInspector with

> /vcl/source/window/window.cxx:3920:26: runtime error: member access within null pointer of type 'WindowImpl'
>     #0 0x2b883bedef80 in vcl::Window::get_id() const /vcl/source/window/window.cxx:3920:26
>     #1 0x2b883f186817 in (anonymous namespace)::findChild(vcl::Window*, rtl::OUString const&, bool) /vcl/source/uitest/uiobject.cxx:399:18
>     #2 0x2b883f185f86 in WindowUIObject::get_child(rtl::OUString const&) /vcl/source/uitest/uiobject.cxx:451:28
>     #3 0x2b883f20e117 in UIObjectUnoObj::getChild(rtl::OUString const&) /vcl/source/uitest/uno/uiobject_uno.cxx:41:45
>     #4 0x2b883f20e4c4 in non-virtual thunk to UIObjectUnoObj::getChild(rtl::OUString const&) /vcl/source/uitest/uno/uiobject_uno.cxx
>     #5 0x2b8879c1ceab in gcc3::callVirtualMethod(void*, unsigned int, void*, _typelib_TypeDescriptionReference*, bool, unsigned long*, unsigned int, unsigned long*, double*) /bridges/source/cpp_uno/gcc3_linux_x86-64/callvirtualmethod.cxx:77:5
>     #6 0x2b8879c171c2 in cpp_call(bridges::cpp_uno::shared::UnoInterfaceProxy*, bridges::cpp_uno::shared::VtableSlot, _typelib_TypeDescriptionReference*, int, _typelib_MethodParameter*, void*, void**, _uno_Any**) /bridges/source/cpp_uno/gcc3_linux_x86-64/uno2cpp.cxx:233:13
>     #7 0x2b8879c13d0d in unoInterfaceProxyDispatch /bridges/source/cpp_uno/gcc3_linux_x86-64/uno2cpp.cxx:413:13
>     #8 0x2b887efde9fa in binaryurp::IncomingRequest::execute_throw(binaryurp::BinaryAny*, std::__debug::vector<binaryurp::BinaryAny, std::allocator<binaryurp::BinaryAny> >*) const /binaryurp/source/incomingrequest.cxx:235:13
>     #9 0x2b887efd861a in binaryurp::IncomingRequest::execute() const /binaryurp/source/incomingrequest.cxx:78:26
>     #10 0x2b887f0b5367 in request /binaryurp/source/reader.cxx:85:9
>     #11 0x2b880b8b0144 in cppu_threadpool::JobQueue::enter(void const*, bool) /cppu/source/threadpool/jobqueue.cxx:100:17
>     #12 0x2b880b8d3f6b in cppu_threadpool::ORequestThread::run() /cppu/source/threadpool/thread.cxx:165:31
>     #13 0x2b880b8dfbcf in threadFunc /include/osl/thread.hxx:185:15
>     #14 0x2b88025206e8 in osl_thread_start_Impl(void*) /sal/osl/unx/thread.cxx:264:9
>     #15 0x2b880438be64 in start_thread (/lib64/libpthread.so.0+0x7e64)
>     #16 0x2b8804cc188c in clone (/lib64/libc.so.6+0xfe88c)

apparently because pParent was non-null but already disposed (so mpWindowImpl
had already been cleared).

I don't know whether this situation can legitimately happen, or was fallout from
an actual error that happened earlier (and went unnoticed), but this is
apparently uitest-only code, so just make it more robust and be done with it.

Change-Id: I178fcf2fb70bf29bc6bbb246ebff5b1933579e5a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/105326
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions