posix: handle another case when we rely on undefined behavior in lseek

[marcinslusarz]

SUMMARY: AddressSanitizer: undefined-behavior src/libpmemfile-posix/lseek.c:234:40 in src/libpmemfile-posix/lseek.c:234:40: runtime error: negation of -9223372036854775808 cannot be represented in type 'pmemfile_off_t' (aka 'long'); cast to an unsigned type to negate this value to itself

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This change is 

[krzycz]

Reviewed 1 of 1 files at r1. Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[codecov-io]

Codecov Report

Merging #322 into master will increase coverage by <.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #322      +/-   ##
==========================================
+ Coverage   78.16%   78.17%   +<.01%     
==========================================
  Files          90       90              
  Lines       13823    13827       +4     
  Branches     1996     1996              
==========================================
+ Hits        10805    10809       +4     
- Misses       2293     2295       +2     
+ Partials      725      723       -2

Impacted Files	Coverage Δ
src/libpmemfile-posix/lseek.c	89.93% <100%> (+0.13%)	:arrow_up:
src/libpmemfile-posix/file.c	66.2% <0%> (-1.38%)	:arrow_down:
src/libpmemfile/path_resolve.c	87.65% <0%> (-1.1%)	:arrow_down:
src/libpmemfile-posix/dir.c	83.29% <0%> (+0.24%)	:arrow_up:
src/libpmemfile-posix/inode.c	77.7% <0%> (+0.34%)	:arrow_up:
src/libpmemfile-posix/rename.c	90.8% <0%> (+0.39%)	:arrow_up:
src/libpmemfile-posix/read.c	93.19% <0%> (+0.68%)	:arrow_up:
tests/posix/mt/mt.cpp	86.45% <0%> (+1.04%)	:arrow_up:
src/libpmemfile-posix/utils.c	73.43% <0%> (+1.56%)	:arrow_up:

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[GBuella]

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Reviewed 1 of 1 files at r2. Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable