Patch to support discid_read_sparse

[coldtobi]

Author: Sebastian Ramacher, see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=736445

In version 0.5.0 of libdiscid discid_read_sparce got added. This
function allows to specify what should be read from the disc. Using this
function one can avoid reading of the MCN of the disc and ISRCs from the
tracks. Only the disc ID is used and nothing else, so it is not
necessary to read the other information.

Please consider applying the attached patch.

[adhawkins]

Manually merged, thanks.