fix: guard against accidental undefined access in Brush (#4504)

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## Description

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Fix brush bug experienced in current release, guard against it in 3.x
too

## Related Issue

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This is interesting... not sure why people use Brush like this? Asked
for a reason in the comment
#2093 (comment)

## Motivation and Context

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bug prevention

## How Has This Been Tested?

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it hasn't really, but it doesn't hurt anything

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## Types of changes

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

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- [ ] My change requires a change to the documentation.
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- [ ] I have added a storybook story or extended an existing story to
show my changes

Co-authored-by: Coltin Kifer <ckifer@amazon.com>

src/cartesian/Brush.tsx

@@ -134,7 +134,7 @@ function TravellerLayer({
     height,
   };
 
-  const ariaLabelBrush = ariaLabel || `Min value: ${data[startIndex].name}, Max value: ${data[endIndex].name}`;
+  const ariaLabelBrush = ariaLabel || `Min value: ${data[startIndex]?.name}, Max value: ${data[endIndex]?.name}`;
 
   return (
     <Layer