soundsource*::ParseHeader discrepancies

[fenugrec]

This patch fixes all kinds of differences in the ::ParseHeader functions
of the sound proxies. The behaviour should now be:

A) returning ERR means the file is invalid, but does *not* imply it has (in)valid tags.
B) setHeaderParsed is set to TRUE at the end of ::ParseHeader to indicate that
 1) the file has been succesfully opened (although not necessarily playable)
 2) tags, *if present*, have been read

The upper levels should call ParseHeader conditionally (i.e. only if getHeaderParsed
returns false) to avoid useless filesystem activity.

Different proxies handle empty tag fields differently (i.e. writing "" or just
not writing anything);
but since each item (artis, title, etc.) should be NULL initially (?), this is
irrelevant.

The initial patch I'm including is based on 1.7 trunk (as of rev ~ 2535) and touches
the following files:
soundsourcem4a.cpp
soundsourcemp3.cpp
soundsourceoggvorbis.cpp
soundsourcesndfile.cpp

the patch also fixes some handles not being closed before returning ERR.

[piloto (dcd2168)]

no audio, no start

[fenugrec (fenugrec)]

piloto: You'll have to provide a bit more info..
-what OS
-what build/branch of mixxx
-was the patch succesful - note that 1.7 is now waaay past 2535 so the patch probably wouldn't work as-is.
-error messages
-etc...

[Sean M. Pappalardo (pegasus-renegadetech)]

Patch applies cleanly to 1.7 branch and tests good for me on MP3 and FLAC files.

[fenugrec (fenugrec)]

Oops, I forgot a set of {} in soundsourceoggvorbis.cpp (lines 271-273)
(fixed in #2257 , thanks Albert)

Here's the equivalent (complete) patch, against 1.8 trunk #2314.
specifically :
ssmp3.cpp;
ssoggvorbis.cpp;
sssoundfile.cpp;

also makes the qDebug messages print out in a more standard format:
qDebug() << "SS[MP3|OV|SNDFILE]::[function]: [error message]";

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/5260