[opt-viewer] Don't except when debug info is not available.

For records without DebugLoc we simply skip the caller location in
map_remarks.

Fixes PR33764.

Patch by Simon Whittaker!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307880 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed