fix vtuner issue

If singleRead(), data read from vtuner demux, has error, writeAll() also cause error and exit main pump thread,
then no more operation is possiible.

https://github.com/openatv/enigma2/commit/464d1316f8894025b5acc216712c2d0be9ccb9f2

Signed-off-by: littlesat <littlesat99@yahoo.com>
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2 into BETA