Fix failure caused by r373247
Fix failure caused by r373247

I incorrectly thought that the 'isLambda' check never fired, so when
splitting up a helper function, I lost the 'nullptr' return value.
ClangD Hover functionality apparently uses this, so the Unittest caught
that.

This patch correctly propogates the nullptr from the helper function.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@373259 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang