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

[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.

llvm-svn: 286331