Double zip_mutex exit in buf_page_get_gen()
|Percona Server||Status tracked in 5.6|
/* The block was buffer-fixed or I/O-fixed while
buf_pool->mutex was not held by this thread.
Free the block that was allocated and retry.
This should be extremely unlikely, for example,
if buf_page_get_zip() was invoked. */
A MySQL 5.6.14 merge regression.