Fix saving hspy file with empty array

[ericpre]

Fix #205

Progress of the PR

• Add support for saving empty array,
• fix closing hspy file when an error occurs,
• [n/a] update docstring (if appropriate),
• [n/a] update user guide (if appropriate),
• add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:rosettasciio build of this PR (link in github checks)
• add tests,
• ready for review.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (dad4914) 86.19% compared to head (cd5c866) 86.21%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
rsciio/hspy/_api.py	73.33%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #206      +/-   ##
==========================================
+ Coverage   86.19%   86.21%   +0.01%     
==========================================
  Files          82       82              
  Lines       10544    10552       +8     
  Branches     2291     2293       +2     
==========================================
+ Hits         9088     9097       +9     
+ Misses        938      935       -3     
- Partials      518      520       +2     

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