Comment 2 for bug 1044823

StacktraceTop:
 unity::dash::previews::CoverArt::SetNoImageAvailable (this=0x4f73850) at /build/buildd/unity-6.4.0/unity-shared/CoverArt.cpp:187
 operator() (this=0x2722c60) at /build/buildd/unity-6.4.0/unity-shared/CoverArt.cpp:171
 std::_Function_handler<bool(), unity::dash::previews::CoverArt::StartWaiting()::<lambda()> >::_M_invoke(const std::_Any_data &) (__functor=...) at /usr/include/c++/4.6/functional:1764
 operator() (this=<optimized out>) at /usr/include/c++/4.6/functional:2161
 unity::glib::Source::SourceCallback (data=<optimized out>, data@entry=<error reading variable: value has been optimized out>) at /build/buildd/unity-6.4.0/UnityCore/GLibSource.cpp:106