hattrie_get assert

[adamyg]

Under the test case of 1M random keys 1 .. 2048 bytes in length, the len == 0 condition within hattrie_get shall be triggered; the resulting bucket type shall be NODE_TYPE_PURE_BUCKET.

assert(*node.flag & NODE_TYPE_PURE_BUCKET || *node.flag & NODE_TYPE_HYBRID_BUCKET);
assert(len > 0);