Empty strings for queries aren't errors
Complain if the config has empty strings
Fix potential race condition when originating CoA requests
Add PW_TYPE_NOT_EMPTY and sprinkle it in the SQL module
Make sql_fetch_row write a pointer to the row instead of setting it inside the handle

The rlm_sql_handle should really be an opaque driver specific struct that the rlm_sql module has no visibility into, this is the first step towards that.