fix problem with `get-module-code'

As reported and fixed by Timur Sufiev

collects/syntax/modcode.rkt

@@ -115,7 +115,7 @@
              [path-d (or main-path-d alt-path-d)]
              [file (if alt-path-d alt-file main-file)]
              [path (if alt-path-d alt-path main-path)]
-             [try-alt? (and (not alt-path-d) (not main-path-d))]
+             [try-alt? (and alt-file (not alt-path-d) (not main-path-d))]
              [get-so (lambda (file)
                        (build-path
                         base sub-path "native"

collects/tests/syntax/modcode.rkt

@@ -0,0 +1,61 @@
+#lang racket
+(require syntax/modcode)
+
+(define dir (find-system-path 'temp-dir))
+(define file.rkt (build-path dir "file.rkt"))
+(define file.ss (build-path dir "file.ss"))
+
+(define compiled-dir (build-path dir "compiled"))
+(make-directory* compiled-dir)
+
+(define (test expect proc . args)
+  (define val (apply proc args))
+  (unless (equal? expect val)
+    (error 'fail "at (apply ~s '~s): ~e is not expected: ~e" proc args val expect)))
+
+(define (try file.sfx src? zo? so?)
+  (printf "trying ~s\n" (list file.sfx src? zo? so?))
+  (define file.zo
+    (let-values ([(base name dir?) (split-path file.sfx)])
+      (build-path base "compiled" (path-add-suffix name #".zo"))))
+  (define file.rkt (path-replace-suffix file.sfx #".rkt"))
+  (define file.so (path-replace-suffix file.sfx #".so"))
+  (when (file-exists? file.ss) (delete-file file.ss))
+  (when (file-exists? file.rkt) (delete-file file.rkt))
+  (when (file-exists? file.zo) (delete-file file.zo))
+  (define ns (make-base-namespace))
+  (dynamic-wind
+   (lambda () (void))
+   (lambda ()
+     (when src?
+       (call-with-output-file*
+        file.sfx
+        (lambda (o)
+          (write '(module file racket/base 10)
+                 o))))
+     (when zo?
+       (call-with-output-file* 
+        file.zo
+        (lambda (o)
+          (write (parameterize ([current-namespace ns])
+                   (compile '(module file racket/base 12)))
+                 o))))
+     (get-module-code file.sfx
+                      #:choose (lambda (src zo so)
+                                 (test src? file-exists? src)
+                                 (test zo? file-exists? zo)
+                                 (test so? file-exists? so)
+                                 #f))
+     (void))
+   (lambda ()
+     (when src? (delete-file file.sfx))
+     (when zo? (delete-file file.zo)))))
+
+(try file.rkt #t #f #f)
+(try file.rkt #t #t #f)
+(try file.rkt #f #t #f)
+(try file.ss #t #f #f)
+(try file.ss #t #t #f)
+(try file.ss #f #t #f)
+
+(delete-directory/files compiled-dir)