CheckLoopVisitor: also visit closure arguments

This turns an ICE on this code:

fn main() {
    |_: [u8; break]| ();
}

from
    'assertion failed: self.tcx.sess.err_count() > 0', librustc_typeck/check/mod.rs
to
    librustc_mir/hair/cx/expr.rs:543: invalid loop id for break: not inside loop scope

which is at a later stage during compilation and most importantly
fixes of bug #50576 will fix this as well.

src/librustc_passes/loops.rs

@@ -82,7 +82,8 @@ fn visit_expr(&mut self, e: &'hir hir::Expr) {
             hir::ExprLoop(ref b, _, source) => {
                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
             }
-            hir::ExprClosure(.., b, _, _) => {
+            hir::ExprClosure(_, ref function_decl, b, _, _) => {
+                self.visit_fn_decl(&function_decl);
                 self.with_context(Closure, |v| v.visit_nested_body(b));
             }
             hir::ExprBlock(ref b, Some(_label)) => {