Relax Beta Encoding requirement to allow 0 bits

[jmthibault79]

Description

I recently added a check to protect against creating Beta Encodings with bitLength 0. This was mistaken, and causes problems reading CRAMs with this parameter - such as those created by htslib for zero-length or constant data series.

This PR reverts that check.

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 #1233 into master will increase coverage by 0.006%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##              master     #1233       +/-   ##
===============================================
+ Coverage     69.331%   69.337%   +0.006%     
- Complexity      8097      8099        +2     
===============================================
  Files            543       543               
  Lines          32472     32472               
  Branches        5498      5498               
===============================================
+ Hits           22513     22515        +2     
  Misses          7751      7751               
+ Partials        2208      2206        -2

Impacted Files	Coverage Δ	Complexity Δ
...mtools/cram/encoding/core/BetaIntegerEncoding.java	100% <100%> (ø)	6 <0> (ø)	⬇️
...dk/samtools/seekablestream/SeekableHTTPStream.java	58.824% <0%> (+1.471%)	14% <0%> (+1%)	⬆️
...va/htsjdk/samtools/sra/SRAIndexedSequenceFile.java	64.865% <0%> (+2.703%)	7% <0%> (+1%)	⬆️

[lbergelson]

This change looks good to me although I don't actually understand why we have files that produce encoders like this.