Fix BQ storage stream split

[RustedBones]

A variable shadowing was introduced here, preventing modification of the stream reader source after splitting.

I don't know the implication of this bug.

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[Abacn]

another bug introduced by seemingly trivial code format cleanup.

[Abacn]

#16721 - to add a cross link to that PR tracking checkframework fix side effects

[RustedBones]

Implication of this bug looks to be limited to cancel not being called on the right stream after subsequent split. No implication on data

[Abacn]

cc: @ahmedabu98 sounds like another place of stale stream leak

[kennknowles]

Implication of this bug looks to be limited to cancel not being called on the right stream after subsequent split. No implication on data

Does this make it excessively hard to test or can a test be added?