RimCase::timeStepDates() returns std::vector<QDateTime> by value, so
calling cbegin() and cend() in separate invocations produced iterators
into two different temporary vectors. Passing these mismatched iterators
to std::find is undefined behavior and walked off freed memory, crashing
in setValidTimeStepRangeForCase().
Snapshot timeStepDates() into a single local vector and use its
iterators. The same pattern was fixed in RimWellConnectivityTable.