Configure: style.
Core: plugged socket leak during configuration test.

This isn't really important as configuration testing shortly ends with
a process termination which will free all sockets, though Coverity
complains.

Prodded by Coverity (CID 400872).
Fixed wrong sizeof() in ngx_http_init_locations().

There is no real difference on all known platforms, but it's still wrong.

Found by Coverity (CID 400876).
Core: removed meaningless check from ngx_palloc_block().

The check became meaningless after refactoring in 2a92804f4109.
With the loop currently in place, "current" can't be NULL, hence
the check can be dropped.

Additionally, the local variable "current" was removed to
simplify code, and pool->current now used directly instead.

Found by Coverity (CID 714236).