fix check of empty description

this is need because _eit_get_string_with_len function return length of
string with size-byte.
Fix assertion in reaper thread
Merge pull request #228 from BtbN/fix_assert

Fix #1539 - assertion in timeshift reaper thread fired due to erroneous size updating
Avoid reordering teletext streams multiple times...

...thus causing continious service restarts
This happens if multiple teletext descriptors point to the same page
Merge remote-tracking branch 'origin/pr/227'
epggrab: add some additional checks in the EIT code for empty strings.
cleanup: remove old files.
support: minor aesthetic change.
dvb: fix disabling of bad muxes caused by dodgy hardware/firmware

because some tuners, mostly USB, can result in ioctl() failures due
to inability to communicate with driver and this was not properly
trapped muxes were being disabled.

Better solution is to reject bad muxes being entered in the first
place based on the tuning capability of the device. Ofc if the
tuner fails to report that correctly (probably) we'll still be
buggered.
Fix #1545 - ensure files only created as required in on-demand mode.
dvb: undo mod to frequency range testing and add additional tuning check

The previous check was garbage because for -S adapters the frequency range
reported by the adapter is in local units (i.e. hi/low band taken into
account) and not simple kHz. This makes checking more difficult and while
its possible I think this should be left for dvb rewrite.

Instead I've re-instated the old code, but muxes are only disable if the
return is EINVAL, which should only be returned if the DVB layer decides
the params are out of range.
Fix #1547 - timeshift: do not create directories until needed

This tries to minimise what is written to disk (inc dirs) when
using on-demand mode. This could result in the failure to write
the buffer not being detected till later and not entirely sure
how clients might handle that.