Change a condition from one to an equivalent one to shut up a
`scan-build` warning about potentially dereferencing a `NULL` value.
This introduces no functional changes, as it’s not actually possible to
dereference a `NULL` value here (but `scan-build` can’t link the
nullability of `error` to the nullability of `result`).

Signed-off-by: Philip Withnall <withnall@endlessm.com>