Add finals for issues raised during review of PR 1091.

[cmnbroad]

Add a few finals, pre request during review of #1091.

[lbergelson]

@cmnbroad Thank you.

[codecov-io]

Codecov Report

Merging #1240 into master will increase coverage by 0.015%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #1240       +/-   ##
===============================================
+ Coverage     69.378%   69.393%   +0.015%     
- Complexity      8107      8108        +1     
===============================================
  Files            544       544               
  Lines          32434     32434               
  Branches        5495      5495               
===============================================
+ Hits           22502     22507        +5     
+ Misses          7732      7728        -4     
+ Partials        2200      2199        -1

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/htsjdk/samtools/CRAMIterator.java	79.72% <ø> (ø)	33 <0> (ø)	⬇️
...dk/samtools/seekablestream/SeekableHTTPStream.java	57.353% <0%> (-1.471%)	13% <0%> (-1%)
...samtools/util/AsyncBlockCompressedInputStream.java	76% <0%> (+4%)	13% <0%> (+1%)	⬆️
...sjdk/samtools/util/Md5CalculatingOutputStream.java	74.359% <0%> (+7.692%)	8% <0%> (+1%)	⬆️