Spotbugs remaining fixes

[lbergelson]

Description

Rebase of https://github.com/samtools/htsjdk/pull/1303

Checklist

• [ ] Code compiles correctly
• [ ] New tests covering changes and new functionality
• [ ] All tests passing
• [ ] Extended the README / documentation, if necessary
• [ ] Is not backward compatible (breaks binary or source compatibility)

[codecov-io]

Codecov Report

Merging #1331 into master will decrease coverage by 0.007%. The diff coverage is 63.636%.

@@               Coverage Diff               @@
##              master     #1331       +/-   ##
===============================================
- Coverage     67.802%   67.795%   -0.007%     
+ Complexity      8252      8251        -1     
===============================================
  Files            562       562               
  Lines          33639     33641        +2     
  Branches        5641      5639        -2     
===============================================
- Hits           22808     22807        -1     
- Misses          8657      8660        +3     
  Partials        2174      2174

Impacted Files	Coverage Δ	Complexity Δ
...java/htsjdk/samtools/MergingSamRecordIterator.java	59.494% <100%> (ø)	19 <0> (ø)	:arrow_down:
...ava/htsjdk/samtools/cram/compression/rans/E14.java	90.566% <100%> (+1.887%)	3 <0> (ø)	:arrow_down:
src/main/java/htsjdk/samtools/util/IOUtil.java	58.213% <100%> (+0.101%)	118 <0> (ø)	:arrow_down:
...n/java/htsjdk/samtools/util/SortingCollection.java	64.444% <100%> (ø)	16 <0> (ø)	:arrow_down:
...tsjdk/tribble/readers/AsciiLineReaderIterator.java	84% <100%> (ø)	6 <0> (ø)	:arrow_down:
...in/java/htsjdk/samtools/TextualBAMIndexWriter.java	66.667% <20%> (-0.866%)	12 <0> (ø)
...samtools/util/AsyncBlockCompressedInputStream.java	72% <0%> (-4%)	12% <0%> (-1%)

[lbergelson]

@tomwhite Thank you!