Initialize refs vector in git_remote_update_tips().
Initialize refs vector in git_remote_update_tips().

Otherwise, bailing out early when ls_to_vector() fails accesses
uninitialized memory.

jflesch/libgit2-mariadb,jflesch/libgit2-mariadb,jflesch/libgit2-mariadb,jflesch/libgit2-mariadb,jflesch/libgit2-mariadb,jflesch/libgit2-mariadb