[clang-tidy] Fix an assertion failure in cppcoreguidelines-pro-type-member-init.

Summary:
The matcher for matching "class with default constructor" still match
some classes without default constructor, which trigger an assert at
Line 307. This patch makes the matcher more strict.

Reviewers: aaron.ballman

Subscribers: nemanjai, cfe-commits

Differential Revision: https://reviews.llvm.org/D25747

llvm-svn: 284727