Fix PR12960 by not attempting to correct cases when we're not actually instantiatiating a template.

This comes up in the begin/end calls of a range-for (see the included test
case). Other suggestions are welcome, though this seems to do the trick without
regressing anything.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157553 91177308-0d34-0410-b5e6-96231b3b80d8