Use strdup not qstrdup to avoid mlt_profile_close free'ing memory allocated with new.
Note: already applied in master. Effectively a cherry pick.
This issue was identified using valgrind. Output:
==200828== Mismatched free() / delete / delete [] ==200828== at 0x4C2E668: free (in /nix/store/270csszcn55xv52pjmvgr6cgy5grc8y5-valgrind-3.14.0/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==200828== by 0xAFCBFD0: mlt_profile_close (in /nix/store/l1dy6sf0sf6j7r7m45sg0xa8i8fxw4zq-mlt-6.13.0/lib/libmlt.so.6.13.0) ==200828== by 0x7E52F8: GLWidget::~GLWidget() (glwidget.cpp:173)