Cosmetic: EVR-CP/Sync Render: Remove unused variables.

Thanks to Snowknight26.
Add support for playing from standard input.

Examples:
 > mpc-hc.exe < sample.ts
 > a_prog.exe | mpc-hc.exe

This commit fixes ticket #3107.
Improve the infinite recursion detection when parsing playlists.

The parser was sometimes too strict and rejected valid playlists.