Added a small try-catch statement for corrupted or empty NIfTI files and test

[shak360]

Added a try-catch block in the isgz function to capture scenarios when NIfTIs are corrupted or empty.

Added a test for this and an empty.nii.gz file.

Deleted NIfTI files that weren't being used in testing (the exact same files were in the test/data folder).

svisagan@Shakthis-Mac-mini NIfTI % cmp -l test/data/example4d.hdr.gz test/example4d.hdr.gz # no output 
svisagan@Shakthis-Mac-mini NIfTI % cmp -l test/data/example4d.img.gz test/example4d.img.gz # no output
svisagan@Shakthis-Mac-mini NIfTI % cmp -l test/data/example4d.nii.gz test/example4d.nii.gz # no output

(The above implies those files were the same. They were also not being used in the code anywhere).

[codecov]

Codecov Report

Merging #51 (8111fea) into master (ad8e822) will decrease coverage by 0.30%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
- Coverage   43.27%   42.97%   -0.31%     
==========================================
  Files           4        4              
  Lines         372      370       -2     
==========================================
- Hits          161      159       -2     
  Misses        211      211              

Impacted Files	Coverage Δ
src/NIfTI.jl	63.80% <100.00%> (-0.44%)	⬇️

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[shak360]

Also minute change, changed seek(io, 0) to seekstart(io)

[Tokazama]

Nice catch

[Tokazama]

Really appreciate this! Once this is merged I'm going to get one more quick commit in and release a patch bump for this.