policies/sourceppa.py: Cache "no PPA" results as well

This accidentally got broken by 11705f4a7.

policies/sourceppa.py

@@ -85,11 +85,11 @@ class SourcePPAPolicy(BasePolicy):
         britney_excuses = self.britney.excuses
         version = source_data_srcdist.version
         sourceppa = self.lp_get_source_ppa(source_name, version)
+        self.source_ppas_by_pkg[source_name][version] = sourceppa
         if not sourceppa:
             return PolicyVerdict.PASS
 
         shortppa = sourceppa.replace(LAUNCHPAD_URL, '')
-        self.source_ppas_by_pkg[source_name][version] = sourceppa
         sourceppa_info[source_name] = shortppa
         # Check for other packages that might invalidate this one
         for friend in self.pkgs_by_source_ppa[sourceppa]:

tests/test_autopkgtest.py

@@ -2052,14 +2052,23 @@ class T(TestBase):
 
         exc = self.do_test(
             [('green', {'Version': '2'}, 'autopkgtest'),
-             ('red', {'Version': '2'}, 'autopkgtest')],
+             ('red', {'Version': '2'}, 'autopkgtest'),
+             ('gcc-5', {}, 'autopkgtest')],
             {'green': (False, {'green': {'i386': 'RUNNING-ALWAYSFAIL', 'amd64': 'RUNNING-ALWAYSFAIL'}}),
-             'red': (False, {'red': {'i386': 'RUNNING-ALWAYSFAIL', 'amd64': 'RUNNING-ALWAYSFAIL'}})},
+             'red': (False, {'red': {'i386': 'RUNNING-ALWAYSFAIL', 'amd64': 'RUNNING-ALWAYSFAIL'}}),
+             'gcc-5': (True, {}),
+            },
             {'green': [('reason', 'block')],
              'red': [('reason', 'source-ppa')]}
         )[1]
         self.assertEqual(exc['red']['policy_info']['source-ppa'], {'red': 'team/ubuntu/ppa', 'green': 'team/ubuntu/ppa'})
 
+        with open(os.path.join(self.data.path, 'data/series-proposed/SourcePPA')) as f:
+            res = json.load(f)
+            self.assertEqual(res, {'red': {'2': 'team/ubuntu/ppa'},
+                                   'green': {'2': 'team/ubuntu/ppa'},
+                                   'gcc-5': {'1': ''}})
+
     def test_sourceppa_missingbuild(self):
         '''Packages from same source PPA get rejected for failed peer FTBFS'''