Fix NegRiskOperatorV2

[mshrieve]

Note

Low Risk
Small, localized change that only adds null checks and warning logs to avoid potential runtime crashes during event handling.

Overview
Adds defensive null handling for MarketResolution.load(...) in handleQuestionReset and handleQuestionResolved: if no entity exists for the given questionID, the handlers now log a warning and return instead of blindly casting and mutating.

This prevents runtime failures on unexpected/ out-of-order QuestionReset/QuestionResolved events and makes the subgraph indexing behavior more resilient.

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