gccrs: fix ice on let else expession

added error handling for let else expression.

Fixes #4375

gcc/rust/ChangeLog:

	* resolve/rust-late-name-resolver-2.0.cc (Late::visit): Visit
	else_expr if has_else_expr, not init_expr.

Signed-off-by: lenny.chiadmi-delage <[email protected]>

Author: Villosse

gcc/rust/resolve/rust-late-name-resolver-2.0.cc

@@ -119,7 +119,7 @@ Late::visit (AST::LetStmt &let)
   ctx.bindings.exit ();
 
   if (let.has_else_expr ())
-    visit (let.get_init_expr ());
+    visit (let.get_else_expr ());
 
   // how do we deal with the fact that `let a = blipbloup` should look for a
   // label and cannot go through function ribs, but `let a = blipbloup()` can?