[BUG] GroupedVirtuoso: empty groups only

[schroda]

Describe the bug

When there are only empty groups, both computeItemKey and itemContent are being called unexpectedly

Example:

groupCounts: [0]

calls:
computeItemKey, 0, 1
itemContent: 0

Reproduction

https://codesandbox.io/p/sandbox/grouped-virtuoso-compute-item-key-out-of-bounds-fwg59s

To Reproduce

Steps to reproduce the behavior:

1. Open codesandbox
2. See console

Expected behavior

Both computeItemKey and itemContent to not get called with a none-existent index

Screenshots

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Desktop (please complete the following information):

• OS: Windows 11 Pro 23H2
• Browser: Edge 144.0.3719.92 (Official Build) (64-Bit)

Additional context
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[oleks12345]

I believe this is same as #985
The computeItemKey is called also for group headers.