Revert "Remove redundant check discovered in post-commit review of r209505."

This breaks with MSVC.
With IsLateTemplateParsed, FunctionDecl::doesThisDeclarationHaveABody() returns true regardless of Body.

This reinstates what was fixed in r208985.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@209896 91177308-0d34-0410-b5e6-96231b3b80d8