Fix for iOS-64 compilation issue

[anna-khakimova]

/Users/itseez/Projects/VMF/vmf-3.0/vmf/3rdparty/xmp/third-party/zlib/gzlib.c:260:24:
error: implicit declaration of function 'lseek' is invalid in C99

[coveralls]

Coverage remained the same at 77.74% when pulling f993d59 on anna-plyakina:fix_MACOS_compilation_issue into e724dd4 on apavlenko:vmf-3.0.

[codecov-io]

Current coverage is 77.74%

Merging #55 into vmf-3.0 will not affect coverage as of 42b56d8

@@            vmf-3.0     #55   diff @@
=======================================
  Files            59      59       
  Stmts          6240    6240       
  Branches          0       0       
  Methods                           
=======================================
  Hit            4851    4851       
  Partial           0       0       
  Missed         1389    1389       

Review entire Coverage Diff as of 42b56d8

---

Uncovered Suggestions

1. +0.15% via ...f_MetadataStream.cpp#823...831
2. +0.13% via ...f_MetadataStream.cpp#785...792
3. +0.09% via ..._vmf_MetadataSet.cpp#24...28
4. See 7 more...

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[apavlenko]

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