[CIR][CodeGen] Fix crash during exception cleanup

[bruteforceboy]

Currently, the following code snippet fails with a crash during CodeGen

class C {
public:
  ~C();
  void operator=(C);
};

void d() {
  C a, b;
  a = b;
}

with error:

mlir::Block* clang::CIRGen::CIRGenFunction::getEHResumeBlock(bool, cir::TryOp): Assertion `tryOp && "expected available cir.try"' failed.

in CIRGenCleanup these lines don't check if there is a TryOp when at the end of the scope chain before getEHResumeBlock is called causing the crash, because it contains an assertion.

This PR fixes this and adds a simple test for a case like this.

[bcardosolopes]

Great, LGTM!