preload: fix utime and utimes for NULL time

[marcinslusarz]

This change is 

[codecov[bot]]

Codecov Report

Merging #405 into master will increase coverage by 0.06%. The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #405      +/-   ##
==========================================
+ Coverage   77.09%   77.16%   +0.06%     
==========================================
  Files          67       67              
  Lines        8493     8499       +6     
  Branches     1698     1700       +2     
==========================================
+ Hits         6548     6558      +10     
  Misses       1515     1515              
+ Partials      430      426       -4

Flag	Coverage Δ
#ltp_tests	46.95% <0%> (-0.5%)	:arrow_down:
#sqlite_tests	46.09% <50%> (+0.16%)	:arrow_up:
#tests_antool	14.95% <0%> (-0.02%)	:arrow_down:
#tests_posix_multi_threaded	26.07% <0%> (+0.01%)	:arrow_up:
#tests_posix_single_threaded	54.61% <0%> (-0.02%)	:arrow_down:
#tests_preload	45.2% <0%> (-0.11%)	:arrow_down:

Impacted Files	Coverage Δ
src/libpmemfile/preload.c	53.97% <50%> (-0.03%)	:arrow_down:
src/libpmemfile-posix/inode.c	88.65% <0%> (+0.34%)	:arrow_up:
src/libpmemfile-posix/dir.c	85.74% <0%> (+0.49%)	:arrow_up:
src/libpmemfile/libpmemfile-posix-wrappers.h	69.76% <0%> (+1.16%)	:arrow_up:
src/libpmemfile-posix/fcntl.c	65.43% <0%> (+2.46%)	:arrow_up:

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[sarahjelinek]

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Reviewed 3 of 3 files at r1. Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable

[sarahjelinek]

Why is codecov so low?

[marcinslusarz]

I had to rebase to resolve conflict. Let's see if it also resolves the problem with coverage (it frequently does).