rbc: fix superfluous rebuilding from scratch - don't abuse self._rbcnamescount The code used self._rbcnamescount as if it was the length of self._names ... but actually it is just the number of good entries on disk. This caused the cache to be populated inefficiently. In some cases very inefficiently. Instead of checking the length before lookup, just try a lookup in self._names - that is also in most cases faster. Comments and debug messages are tweaked to help understanding the issue and the fix.