Fix I/O of variants with empty info/individual fields

[alumi]

Summary

This PR fixes three minor bugs in VCF/BCF I/O

1. Writing :info {} does not emit . (VCF)
   

   cljam/test/cljam/io/vcf/writer_test.clj

   Lines 50 to 51 in f91f816

   	{:chr "2", :pos 2, :ref "N", :info {}}
   	"2\t2\t.\tN\t.\t.\t.\t.\t.\t.\t.\n"

2. Writing a variant map without samples will cause a NPE (VCF)
   

   cljam/test/cljam/io/vcf/writer_test.clj

   Lines 62 to 63 in f91f816

   	{:chr "6", :pos 6, :ref "N", :info {:XA "6"}, :FORMAT [:XB], :SAMPLE01 {}}
   	"6\t6\t.\tN\t.\t.\t.\tXA=6\tXB\t.\t.\n")))

3. Omitted genotype fields are totally ignored (VCF/BCF)
   e.g. Reading DP:HQ 4:51,51 2 does not assoc :HQ nil to the 2nd sample.
   

   cljam/test/cljam/test_common.clj

   Lines 711 to 714 in f91f816

   	:FORMAT [:GT :GQ :DP :HQ],
   	:NA00001 {:GT "1|2", :GQ 21, :DP 6, :HQ [23 27]},
   	:NA00002 {:GT "2|1", :GQ 2, :DP 0, :HQ [18 2]},
   	:NA00003 {:GT "2/2", :GQ 35, :DP 4, :HQ nil}}

Tests

• lein check 🆗
• lein test :all 🆗
• lein cloverage 🆗
• lein eastwood 🆗

[codecov]

Codecov Report

Merging #167 into master will increase coverage by 0.02%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##           master     #167      +/-   ##
==========================================
+ Coverage   86.51%   86.53%   +0.02%     
==========================================
  Files          73       73              
  Lines        5619     5624       +5     
  Branches      492      491       -1     
==========================================
+ Hits         4861     4867       +6     
  Misses        266      266              
+ Partials      492      491       -1

Impacted Files	Coverage Δ
src/cljam/io/vcf/util.clj	92.85% <100%> (+0.54%)	⬆️
src/cljam/io/bcf/reader.clj	92.52% <75%> (ø)	⬆️

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[athos]

LGTM 👍

[r6eve]

LGTM! Thank you for the consideration.

[alumi]

Thank you for reviewing @athos @r6eve! 😃