[clang] [clang][Rewriter] Adjust end offset before RewriteBuffer::getMappedOffset() call (PR #187374)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 approved this pull request.

Makes sense to me, but I'm not super familiar with this piece of code.

https://github.com/llvm/llvm-project/pull/187374