Since gmnlm loads the bookmarks file at launch if no gemini URL was
passed in, as it stands running gmnlm for the first time gives this
error:

Error opening /home/cactus/.local/share/gmni/bookmarks.gmi for
writing: No such file or directory
Assertion failed: uc == CURLUE_OK (src/gmnlm.c: do_requests: 673)
Aborted

This is easily solved by users, but since the mechanism already exists
within gmnlm to create that directory itself (and is used by
save_bookmark), users shouldn't have to be the ones to fix it.
I tried writing a patch for this myself, but wound up in a sea of
other issues that I didn't fully understand.