Add a check for prog_id to fix bad last of the day/first of the day merges

[kyl416]

If the prog_id is unique, it means it's a seperate episode and shouldn't be merged

I came across this issue when testing the new tvgids.tv/gids.tv replacement source since episode titles are not available from the base pages, so it incorectly merged a bunch of 05:30 and 06:00 shows into an hour long 05:30-06:30 block.