Description of problem:
PackageKit crashes

Version-Release number of selected component (if applicable):
libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64
PackageKit-1.1.12-11.fc31.x86_64

How reproducible:
always

Steps to Reproduce:
1. dnf copr enable rpmsoftwaremanagement/dnf-nightly
2. dnf distro-sync
3. systemctl restart packagekit

Additional info:
$ coredumpctl debug
(gdb) bt
#0  libdnf::ConfigMain::addVarsFromEnv(std::map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >&) (varsMap=std::map with 0 elements)
    at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/conf/ConfigMain.cpp:632
#1  0x00007feb1ec4b39c in libdnf::dnf_context_load_vars(_DnfContext*) (context=<optimized out>) at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/dnf-context.cpp:2536
#2  0x00007feb1ec55498 in dnf_repo_setup(DnfRepo*, GError**) (repo=repo@entry=0x5588fdeb7220, error=error@entry=0x7ffe3711fb48)
    at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/dnf-repo.cpp:1150
#3  0x00007feb1ec511f4 in dnf_repo_loader_repo_parse_id
    (error=0x7ffe3711fb48, keyfile=0x5588fe009180, filename=0x5588fdec28f0 "/etc/yum.repos.d/fedora-rawhide-modular.repo", id=0x5588fe005860 "rawhide-modular", self=0x5588fde8a750)
    at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/dnf-repo-loader.cpp:349
#4  dnf_repo_loader_repo_parse (error=0x7ffe3711fb48, filename=0x5588fdec28f0 "/etc/yum.repos.d/fedora-rawhide-modular.repo", self=0x5588fde8a750)
    at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/dnf-repo-loader.cpp:380
#5  dnf_repo_loader_refresh(DnfRepoLoader*, GError**) (self=0x5588fde8a750, error=0x7ffe3711fb48) at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/dnf-repo-loader.cpp:425
#6  0x00007feb1ec51962 in dnf_repo_loader_get_repos(DnfRepoLoader*, GError**) (self=0x5588fde8a750, error=0x7ffe3711fb48)
    at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/dnf-repo-loader.cpp:476
#7  0x00007feb1ec49e6f in dnf_context_setup(DnfContext*, GCancellable*, GError**) (context=0x5588fdea03d0, cancellable=<optimized out>, error=0x7ffe3711fb48)
    at /usr/src/debug/libdnf-0.35.6-0.25gf4c497d4.fc31.x86_64/libdnf/dnf-context.cpp:1950
#8  0x00007feb1ee15615 in pk_backend_setup_dnf_context () at /usr/lib64/packagekit-backend/libpk_backend_dnf.so
#9  0x00007feb1ee1576f in pk_backend_ensure_default_dnf_context () at /usr/lib64/packagekit-backend/libpk_backend_dnf.so
#10 0x00007feb1ee1c9bf in pk_backend_initialize () at /usr/lib64/packagekit-backend/libpk_backend_dnf.so
#11 0x00005588fcb0b013 in pk_backend_load ()
#12 0x00005588fcb18d8b in pk_engine_load_backend ()
#13 0x00005588fcafd108 in main ()