Fixing exception in bar chart with stack mode when no data is present.

[dennisoelkers]

Description

Motivation and Context

This change is fixing an issue which results in an exception being thrown when a bar chart visualization in stack mode has no data.

/nocl No user-facing change yet.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.