Fix return value in StreamReader::read

Review Request #100701 - Created Feb. 21, 2011 and submitted - Latest diff uploaded

Kamil Klimek
phonon, phonon-backends
length parameter was treated as required size to read. It caused for files with id3v1 tags to end playback at begining of the file, because ret value was treated by libvlc as error. Reading id3v1 tags caused to seek almost to end of file and read not as much data as was put in length parameter. After returning length > 0 (we read at least something) everything started to work fine.