Fix regression when dealing with generics/values with unresolved inference
Follow up for rust-lang/rust#151703, fixing regression caused in rollup rust-lang/rust#152825
Forgot to handle generics & unresolved inference variables (as in `get_safe_transmute_error_and_reason`) in my previous PR. This followup checks for them before trying to normalize.
I am not completely sure its right approach to have this check cloned but as `select_transmute_obligation_for_reporting` fn just chooses obligation and doesn't actually return an error, this check shouldn't be removed from `get_safe_transmute_error_and_reasnon`. If there is any better solution, let me kmow.
Fixes: rust-lang/rust#153755
r? @jdonszelmann
Trevor Gross
68d2666fc2