So, apparently, *this can be NULL sometimes.

Fixes #9078.

And the clang sayeth, "verily, in well-defined C++ code, the 'this'
pointer cannot be null!". And, in reply, we respondeth, "our C++ code be
not well-defined." Amen.
Merge pull request #9081 from narc0tiq/this-is-null-sparta

So, apparently, *this can be NULL sometimes.