ARROW-5314: [Go] Fix bug for FixedSizeBinary with offset

[alexandreyc]

Same thing as #4307 but for FixedSizeBinary

[codecov-io]

Codecov Report

Merging #4334 into master will decrease coverage by 16.05%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master    #4334       +/-   ##
===========================================
- Coverage   88.24%   72.19%   -16.06%     
===========================================
  Files         777       71      -706     
  Lines       97882     5944    -91938     
  Branches     1251        0     -1251     
===========================================
- Hits        86373     4291    -82082     
+ Misses      11273     1425     -9848     
+ Partials      236      228        -8

Impacted Files	Coverage Δ
go/arrow/array/fixedsize_binary.go	74.41% <100%> (+0.6%)	⬆️
python/pyarrow/ipc.pxi
cpp/src/arrow/csv/chunker-test.cc
cpp/src/parquet/column_page.h
cpp/src/parquet/bloom_filter-test.cc
cpp/src/arrow/array/builder_decimal.cc
cpp/src/plasma/client.cc
cpp/src/arrow/io/test-common.h
cpp/src/arrow/util/int-util-test.cc
cpp/src/arrow/python/io.cc
... and 697 more

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[sbinet]

LGTM.

(ah! when #4307 hit the fan, true to my motto "bugs are like mushrooms, find one? look around, there should be many others", I immediately looked at array.Binary. but didn't think about FixedSizeBinary)

thanks!

[alexandreyc]

I think it's worth a second pass to be sure we did not forget another :)