Don't signal an error when encountering invalid rust syntax. Without
this patch, invalid rust code would prevent a chunk of the buffer from
being highlighted (bug#79272).
* lisp/progmodes/rust-ts-mode.el (rust-ts-mode--fontify-scope):
(rust-ts-mode--fontify-pattern): Avoid calling `string-match-p' on nil
when a node is missing a parent.
* test/lisp/progmodes/rust-ts-mode-resources/font-lock-no-parent.rs:
Rust file that reproduces the issue.
* test/lisp/progmodes/rust-ts-mode-tests.el: Test case to reproduce the
issue.
