media: dvb: Protect against removing all PIDs from an active filter

When TS filter is active (running), it is not allowed to remove
all PIDs associated with the filter; The filter state would be
invalid and as such may result in unexpected behavior while
performing runtime operations on the filter.

CRs-Fixed: 492444
Change-Id: I340b02bed218e89ffe89932e3b3e9ea93f429876
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>
Signed-off-by: Sridhar Gujje <sgujje@codeaurora.org>