Cleanup tc-app-objects a bit.

collects/typed-racket/typecheck/tc-app/tc-app-objects.rkt

@@ -53,17 +53,16 @@
             n (stringify tnames)))
          (for-each (match-lambda
                      [(list tname tfty opt?)
-                      (let ([s (dict-ref name-assoc tname
+                      (define s
+                        (dict-ref name-assoc tname
                           (lambda ()
                             (unless opt?
                               (tc-error/delayed "value not provided for named init arg ~a"
                                                 tname))
-                                   #f))])
-                        (if s
-                            ;; this argument was present
-                            (tc-expr/check s (ret tfty))
-                            ;; this argument wasn't provided, and was optional
-                            #f))])
+                            #f)))
+                      ;; Only check the argument if it is provided
+                      (when s
+                        (tc-expr/check s (ret tfty)))])
                    tnflds)
          (ret (make-Instance c))]
         [(tc-result1: t)