[index] Fix issue with protocol name locations in conformance list of an ObjC class...

[index] Fix issue with protocol name locations in conformance list of an ObjC class when they come from a typedef.

The ObjC class protocol list assumes there is an associated location for each protocol but no location is provided
when the protocol list comes from a typedef, and we end up with a buffer overflow when trying to get locations for the protocol names.

Fixes crash of rdar://28980278.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@286331 91177308-0d34-0410-b5e6-96231b3b80d8