[include-fixer] Don't return a correction if the header insertion failed.

This is could happen in cases involving macros and we don't want to
return an invalid fixit for it or a confusing error message with no
fixit.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@292405 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed