In `bp_blogs_record_existing_blogs()`, use `$wpdb->blogid` rather than hardcoded `1` as there is no guarantee what the current blog ID actually is, even on single-site installations. See #5749.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8586 cdf35c40-ae34-48e0-9cc9-0c9da1808c22