Fix stack output for SLOAD

[OlivierBBB]

SLOAD must only write to the stack if unexceptional. This simplifies the tracing (in case of an SLOAD that raises the OOGX flag and attempts to load a nonzero value from storage.)

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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}