More robust implementation of MPEG frame header search. The parser will not only...

More robust implementation of MPEG frame header search. The parser will not only search for the very first byte sequence that looks like a valid MPEG frame header. It will search for a valid MPEG frame header sequence, decode it, and probe if there is a consecutive MPEG frame header of the same type (MPEG version, layer, sampling frequency) at the expected position. This approach will reduce false detection of MPEG frame headers in case of errorous metadata or garbaged files. Fixes FS#12007.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29603 a1c6a512-1295-4272-9138-f99709370657