Patch: avpair.c - empty reply VALUE_PAIR (0x0) for replies with unknown vendor attributes

Hello again, when the RADIUS servers sends a reply packet with an attribute for an unknown vendor freeradius-client just skips over this when filling response VALUE_PAIR list. Unfortunately it doesn't for unknown attributes from known vendors - in that case rc_avpair_gen returns NULL in the first recursion which results in a NULL pointer for reply VALUE_PAIR. The attached patch just skips over unknown attributes for known vendors just like the lib skips over attributes from unknown vendors. Rgds, Stefan