Allow using empty array when indexing on DataStub object

[ehennestad]

Fix #595

Motivation

Fix issue.

How to test the behavior?

See issue #595

Example that works after the fix, but not before:

nwb = NwbFile(...
    'identifier', 'DATASTUB',...
    'session_description', 'test datastub object copy',...
    'session_start_time', datetime());

% Add different datatypes to a table, and try to read them in later
% using empty indexing on a DataStub representation
tableToExport = table( ...
    {'test'}, ... % Cell
    0, ... % Double
    false, ... % Logical
    struct('x', 1, 'y', 1, 'z', 1) ... % Struct (compound)
);
dynamicTable = util.table2nwb(tableToExport);
nwb.acquisition.set('Test', dynamicTable);

nwbExport(nwb, 'testLoadWithEmptyIndices.nwb')

nwbIn = nwbRead('testLoadWithEmptyIndices.nwb', 'ignorecache');

importedTable = nwbIn.acquisition.get('Test');
varNames = transpose( string(importedTable.colnames) );

for iVarName = varNames
    iDataStub = importedTable.vectordata.get(iVarName).data;

    assert(isa(iDataStub, 'types.untyped.DataStub'))
    value = iDataStub([]);
    assert(isempty(value))
    
    if isstruct(tableToExport.(iVarName))
        expectedClass = 'table';
    else
        expectedClass = class(tableToExport.(iVarName));
    end
    assert(isa(value, expectedClass))
end

Checklist

• Have you ensured the PR description clearly describes the problem and solutions?
• Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[ehennestad]

@lawrence-mbf I would value your input here.

The proposed fix works in the specific situation, but if you have ideas on how to improve this, or if there are things I have overlooked please let me know.

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes missing coverage. Please review.

Project coverage is 95.39%. Comparing base (c3eedb7) to head (e3cfe50).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
+types/+untyped/@DataStub/load_mat_style.m	76.92%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #605      +/-   ##
==========================================
- Coverage   95.44%   95.39%   -0.05%     
==========================================
  Files         137      137              
  Lines        5265     5277      +12     
==========================================
+ Hits         5025     5034       +9     
- Misses        240      243       +3     

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