595 Allow using empty indices for datastub

[ehennestad]

Fix #595

Motivation

Fix issue.

How to test the behavior?

See issue #595

Checklist

• [x] Have you ensured the PR description clearly describes the problem and solutions?
• [x] Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• [x] 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[bot]]

Codecov Report

Attention: Patch coverage is 15.38462% with 11 lines in your changes missing coverage. Please review.

Project coverage is 90.42%. Comparing base (bc4b87d) to head (1b4dbfb).

Files with missing lines	Patch %	Lines
+types/+untyped/@DataStub/load_mat_style.m	15.38%	11 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #605 +/- ## ========================================== - Coverage 90.63% 90.42% -0.22% ========================================== Files 106 106 Lines 4686 4698 +12 ========================================== + Hits 4247 4248 +1 - Misses 439 450 +11 ``` | [Flag](https://app.codecov.io/gh/NeurodataWithoutBorders/matnwb/pull/605/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NeurodataWithoutBorders) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/NeurodataWithoutBorders/matnwb/pull/605/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NeurodataWithoutBorders) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NeurodataWithoutBorders#carryforward-flags-in-the-pull-request-comment) to find out more.

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