Removed AVC_TS_NA_T/H264_720p_210s_TTS.ts from convert-dlna-scaled-helper.sh

H264_720p_210s_TTS_indx.txt starts with a time offset of 4596834 for some
 reason. It's redundant anyway with AVC_TS_NA_T/H264_720p_240s_TTS.ts.
Made more improvements to indexConvert to deal with some DLNA reference index file issues

indexConvert will now add a 0-time entry at the start of the odid index
 file when one isn't present on a forward-rate DLNA reference index file or
 at the end of the odid index file for negative-rate index file.

Added special-case logic to deal with the errant offset values for the
 negative-rate B-LPCM-L-04 index files. The values in these indexes appear
 to be the 32-bit 2's compliment of the real values. This should be bugged
 and the logic removed when the issue is addressed.

Added logic to exclude index entries with a byte offset equal to the
 preceding index entry. These are illegal in odid index files. And they
 only serve to misrepresent the time range in a DLNA TimeSeekRange response.

Tested by invoking convert-dlna-scaled-helper.sh. Spot checks on the
 log output and some of the produced index files checked out. But testing
 continues...