The commit splitting out the qemuSnapshotRevertInactive function
dropped the 'defined = true' line by accident and instead
returned -1, leaving the user with a cryptic error:
error: An error occurred, but the cause is unknown
https://bugzilla.redhat.com/show_bug.cgi?id=2039136https://gitlab.com/libvirt/libvirt/-/issues/266
Fixes: 85e4a13c3f19078fb6af5ffb4a80022c142cbc7e
Signed-off-by: Ján Tomko <jtomko@redhat.com>