[llvm] [RISCV][TTI] Add checks for invalid cast operations (PR #88854)

[Philip Reames via llvm-commits]

preames wrote:

If I'm reading the code and discussion right, the LV is querying a truncate with result wider than source?  If so, this does not seem like the right fix.  If LV is querying an invalid argument combination, that's a LV bug and should be fixed as such.  

https://github.com/llvm/llvm-project/pull/88854