lib/repo: fix leak of `bootloader` field
lib/repo: fix leak of `bootloader` field

Added in 21ebc7d21edd00c3fe0ce80ea68ba3f8f5e41ae3

Closes: #1837
Approved by: rfairley

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree