[llvm] [Support] Fix UB in decodeULEB128 and decodeSLEB128 (NFC) (PR #114986)

[Mingming Liu via llvm-commits]

minglotus-6 wrote:

A drive-by comment, I wonder if it makes sense to add unit test coverage for `decodeULEB128` and `decodeSLEB128` in  llvm/unittests/Support/LEB128Test.cpp?

https://github.com/llvm/llvm-project/pull/114986