HS: parse-cmd at-end? guard + catch do-wrap fix asyncError (+2 tests)

- parser.sx: parse-cmd true-fallback returns nil when at-end? instead of
  calling parse-expr at EOF — fixes trailing 'then' causing compilation
  error for 'on ... then' terminated handlers
- compiler.sx: catch-without-finally branch wraps guard+reraise in do so
  both expressions are sequenced inside the let binding

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/hyperscript/parser.sx

@@ -2872,14 +2872,17 @@
               ((and (= typ "keyword") (or (= val "on") (= val "init") (= val "def") (= val "behavior") (= val "live") (= val "when") (= val "bind")))
                 nil)
               (true
-                (let
-                  ((expr (parse-expr)))
+                (if
+                  (at-end?)
+                  nil
                   (let
-                    ((callable? (if (and (dict? expr) (get expr :hs-ast)) (= (get expr :kind) "call") (or (= (first expr) (quote call)) (= (first expr) (quote method-call))))))
-                    (if
-                      (or callable? hs-span-mode)
-                      expr
-                      (error "Invalid command — expected a function call")))))))))
+                    ((expr (parse-expr)))
+                    (let
+                      ((callable? (if (and (dict? expr) (get expr :hs-ast)) (= (get expr :kind) "call") (or (= (first expr) (quote call)) (= (first expr) (quote method-call))))))
+                      (if
+                        (or callable? hs-span-mode)
+                        expr
+                        (error "Invalid command — expected a function call"))))))))))
       (define
         parse-cmd-list
         (fn