[clang] [Clang] Fix crash when -header-include-filtering is not specified (PR #136232)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

I think so. Even if this gets diagnosed more clearly by the driver, users can bypass that using `-Xclang`. Even for me as a Clang developer this message would be confusing, especially in more complex scenarios (e.g. with response files involved).

https://github.com/llvm/llvm-project/pull/136232