[clang-tidy] Fix invalid location in readability-misleading-indentation diagnostic

Before this patch readability-misleading-indentation could issue diagnostics
with an invalid location, which would lead to an assertion failure in
ClangTidyContext::diag()

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@358589 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed