tracbuildbot/buildbot_cache.py: async_buildbot_cache_worker() - fix - when error of caching of one builder interrupts whole caching.
tracbuildbot/buildbot_cache.py: async_buildbot_cache_worker() - fix - when error of caching of one builder interrupts whole caching.

trac-hacks/tracbuildbot,trac-hacks/tracbuildbot,trac-hacks/tracbuildbot