Rollup merge of #152661 - BartSimpson001:fix-next-solver-from-ice, r=petrochenkov

Avoid ICE in From/TryFrom diagnostic under -Znext-solver

Fixes rust-lang/rust#152518.

Under `-Znext-solver=globally`, `trait_ref.args` may contain fewer
elements than expected. The diagnostic logic in
`fulfillment_errors.rs` assumed at least two elements and
unconditionally called `type_at(1)`, which could lead to an
index out-of-bounds panic during error reporting.

This change adds a defensive check before accessing the second
argument to avoid the ICE. A UI regression test has been added.

Author: Zalathar