[clang-format] Fix the crash when formatting unsupported encodings

Fixes PR33946

Differential Revision: https://reviews.llvm.org/D61559

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@360257 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed