Fix error handling in drizzle_binlog_get_filename
Fix error handling in drizzle_binlog_get_filename

In addition the function returns DRIZZLE_RETURN_OK
when no binlog files were available on the server.

Instead use `drizzle_set_error` and return
status DRIZZLE_RETURN_NOT_FOUND.

sociomantic/libdrizzle-redux,sociomantic/libdrizzle-redux,sociomantic/libdrizzle-redux