Verify if an expr contains errors before checking invertibility

[secure-sw-dev-bot]

This issue was copied from microsoft/checkedc-clang#1154

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The community has introduced a new annotation called "contains-errors" on AST
nodes that contain semantic errors. As a result, after the upgrade of Checked C
sources to LLVM 12 we need to check if an expr contains errors before operating
on the expr. One such place is in InverseUtil::IsInvertible where we need to
check if the input modifying expr contains errors.

This fixes microsoft/checkedc-clang#1153