This more closely matches the intended, documented behaviour of this
method. The previous implementation was incorrectly checking
`sampleDataEnd + newSampleSize`, but it's more correct to compare
`existingSampleDataLength + newSampleSize`, in order to handle the
case of non-zero `sampleDataStart`. We've already checked above whether
`newSampleSize` fits after `sampleDataEnd` without growing or
reshuffling the array, so no need to basically repeat that check.
In the case of handling one sample at a time, the previous
implementation resulted in `sampleData` growing by `sampleSize`
**every time** the pointers reached the end. With the new check for
`sampleDataStart == sampleDataEnd`, this is avoided by always writing
each new sample at the start of the array (because the previous sample
has already been consumed), meaning `sampleData` remains equal to
`sampleSize` without growing.
PiperOrigin-RevId: 593119927
64231ee079