on export to .ods

Thread 1:

5  0x00007f758fde4969 in raise () from /lib64/libc.so.6
6  0x00007f758fde5f98 in abort () from /lib64/libc.so.6
7  0x00007f758f485afd in __gnu_debug::_Error_formatter::_M_error (
   this=0x7f7588872860 <__gnu_debug::_Error_formatter::_M_at(char const*, unsigned int)::__formatter>)
   at ../../../.././libstdc++-v3/src/c++11/debug.cc:1069
8  0x00007f7587b42922 in __gnu_debug::_Safe_iterator<std::__detail::_Node_iterator<ImpGraphic*, true, false>, std::__debug::unordered_set<ImpGraphic*, std::hash<ImpGraphic*>, std::equal_to<ImpGraphic*>, std::allocator<ImpGraphic*> > >::operator++ (
   this=0x7f755a58e440) at /srv/crashtestdata/gccbuild/gcc8/include/c++/8.2.0/debug/safe_iterator.h:295
9  0x00007f7587b415d5 in vcl::graphic::Manager::registerGraphic (this=0x5fe9860,
   pImpGraphic=std::shared_ptr<ImpGraphic> (use count 1, weak count 0) = {...})
   at /home/buildslave/source/libo-core/vcl/source/graphic/Manager.cxx:123
10 0x00007f7587b418e2 in vcl::graphic::Manager::newInstance (this=0x5fe9860)
   at /home/buildslave/source/libo-core/vcl/source/graphic/Manager.cxx:156
11 0x00007f758798c406 in Graphic::Graphic (this=0x7f755a58e6d0)
   at /home/buildslave/source/libo-core/vcl/source/gdi/graph.cxx:187
12 0x00007f758799c85a in ImpGraphic::loadPrepared (this=0x80d2500)
   at /home/buildslave/source/libo-core/vcl/source/gdi/impgraph.cxx:1540
13 0x00007f758799c999 in ImpGraphic::ImplSwapIn (this=0x80d2500)
   at /home/buildslave/source/libo-core/vcl/source/gdi/impgraph.cxx:1561
14 0x00007f758799c813 in ImpGraphic::ensureAvailable (this=0x80d2500)

and a bunch of other threads looking like they've just come from the same
family of methods

Change-Id: Ic13d3c7cb2fb4adaa2a0a6b8845fc2156d53005e
Reviewed-on: https://gerrit.libreoffice.org/70271
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>