Type-checking an operator requires look up of all of its decls regardless of
which access modifier is used before filtering. If one of them is a package
decl in an imported module that was built with package-name, but the use site
of the operator decl is in a module that is not built with package-name, it
currently crashes as it tries to access package context of the use site, which
is null. This PR checks if both decl site and use site have package contexts
before accessing the package name property, otherwise return false to be filtered
out.
Resolves rdar://108961906
