[llvm] Modify llvm-gsymutil to ignore invalid file indexes. (PR #70876)

[Greg Clayton via llvm-commits]

clayborg wrote:

> @clayborg, the gsym side change looks good to me. How does lldb work in this case? Will it crash or have similar check to emit warning/error?

LLDB handles the case of file indexes being out of range without crashing. We don't emit an error each time we see this as if we did, we would most likely spew a ton of error messages to the console which isn't user friendly.

https://github.com/llvm/llvm-project/pull/70876