Bugfix: foo and foo_ names cause incorrect prefix calculation

[azidar]

Problem

When naming foo, then foo_, the calculation for the prefix of foo_ is incorrect. It should not have a prefix, but instead thinks the entire foo_ is the prefix. When the prefix is stripped to find the index, you get a java.lang.NumberFormatException: For input string: "", as it tries to convert the empty string to an Int.

This bugfix checks the case where a prefix is calculated, but would return an empty string if stripped.

Contributor Checklist

• [N/A] Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• [N/A] Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Bugfix

Desired Merge Strategy

• Squash: The PR will be squashed and merged (choose this if you have no preference).

Release Notes

Naming foo and then foo_ will no longer trigger an error.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.5.x, 3.6.x, or 5.x depending on impact, API modification or big change: 6.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[jackkoenig]

LGTM although left a suggested improvement