obexd/pbap: clear cache if name header is present

Remote device is not able to fetch call logs from different folder.
It always returns the call logs requested in first request.

Considering a situation to fetch from och and then from cch,
there are two ways to request x-bt/vcard-listing:
Case I:
1. SetPhoneBook to /telecom/och (absolute path)
2. PullvCardListing with name header '' (empty)
Remote devices using this method always calls SetPhoneBook with absolute path
to set the path and we clear the cache when new path is set.
Case II:
1. SetPhoneBook to /telecom (relative path)
2. PullvCardListing with name header 'och'
Remote devices using this method calls SetPhoneBook with '/telecom' only once
and cache is not cleared when second PullvCardListing is made with name header.
This results in cached incorrect list sent to remote device.

Clear cache if name header is present would prevent sending of
cache list as it is not present. Instead it would request to
create new cache based on new name header.
1 file changed