In a libary of whole-album (i.e. multi-track) flac files, having an even number 
of flacs causes Slimserver to mistakenly assign too many contributors to each 
track.

Tested version: Slimserver 6.2 svn 4452

Steps to reproduce the bug:

1). Download the posted zip file and extract the test flac files to a folder.
2). Set Slimserver's music folder to the folder containing the test files.
3). Perform a "Clear library and rescan everything."
4). Browse the music folder to h_Classical/Beethoven, L/String Quartets - 
Takács - D1 - Op. 18, Nos. 1, 2, 3.flac 
5). Observe that tracks in this flac file get up to 3 "Beethoven, L"s assigned 
to ARTIST and COMPOSER
6). Browse other flac files in the music folder hierarchy, observe that 
multiple ARTISTs and COMPOSERs are being assigned.
6). Kill simserver
7). Rename any flac file in the music folder hierarchy to end with ".not" so 
slimserver won't scan the file, so we will now have an odd number of total 
albums in the library.
8). Restart slimserver, clear and rescan library.
9). Browse music folder hierarchy and observer that all tracks get only a 
single ARTIST and COMPOSER assigned (the correct behavior).