Allow returns when API on licensepool is None (#22)

* Allow returns when API on licensepool is None

In the case where we are pulling in ACSM files, they are not
open access, but they also have no API assoicated. So we should
allow a return.

* Allow return of ACSM content.

api/circulation.py

@@ -1017,8 +1017,8 @@ def revoke_loan(self, patron, pin, licensepool):
             on_multiple='interchangeable'
         )
         if loan:
-            if not licensepool.open_access and not licensepool.self_hosted:
-                api = self.api_for_license_pool(licensepool)
+            api = self.api_for_license_pool(licensepool)
+            if not (api is None or licensepool.open_access or licensepool.self_hosted):
                 try:
                     api.checkin(patron, pin, licensepool)
                 except NotCheckedOut, e:

tests/test_circulationapi.py

@@ -960,7 +960,8 @@ def yes_we_can(*args, **kwargs):
 
     @parameterized.expand([
         ('open_access', True, False),
-        ('self_hosted', False, True)
+        ('self_hosted', False, True),
+        ('neither', False, False),
     ])
     def test_revoke_loan(self, _, open_access=False, self_hosted=False):
         self.pool.open_access = open_access