FIX: Use successfully loaded metadata only

FIX: Use successfully loaded metadata only

Values greater than 0, means error. We exit from loop on error
with empty super-block pointer when sd pointer is valid.
This cannot be detected by check condition as error.
For sure we shouldn't go forward with error condition.
It leads to throwing exception with core file when metadata handler
wants to access non existing super-block.

Signed-off-by: Adam Kwolek <adam.kwolek@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>