[Sema] Don't crash when recovering from a misspelled pseudo destructor call to an incomplete type.

When attempting to correct a misspelled pseudo destructor call as in:

struct Foo;
void foo(Foo *p) {
  p.~Foo();
}

a call is made in canRecoverDotPseudoDestructorCallsOnPointerObjects
to LookupDestructor without checking that the record has a definition.

This causes an assertion later in LookupSpecialMember which assumes that
the record has a definition.

Patch By Roman Zhikharevich!

Differential Revision: https://reviews.llvm.org/D57111

Reviewed By: riccibruno

llvm-svn: 352047