sp: add flb_errno() after flb_calloc failure.
sp: add flb_errno() after flb_calloc failure.

This commit adds flb_errno() in several places after the flb_calloc
returns null, for better error handling.
This also addresses review comment.

Signed-off-by: Yong Tang <765086fe2e0c1f980161f127fec596800f327f62@outlook.com>

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