Fix errors in license compliance dialog

src/pretix/base/views/source.py

@@ -36,4 +36,4 @@ def get_source(request):
         n = d.get('source_notice', '')
         return render(request, 'source.html', {'notice': n})
     else:
-        raise Http404(f'Not used under AGPL ({d["base_license"]})')
+        raise Http404(f'Not used under AGPL ({d.get("base_license")})')

src/pretix/control/views/global_settings.py

@@ -134,7 +134,10 @@ class LicenseCheckView(StaffMemberRequiredMixin, FormView):
             seen = set()
             for entry_point in pkg_resources.iter_entry_points(group='pretix.plugin', name=None):
                 if entry_point.dist.key not in seen:
-                    license, url = self._get_license_for_pkg(entry_point.dist.key)
+                    try:
+                        license, url = self._get_license_for_pkg(entry_point.dist.key)
+                    except FileNotFoundError:
+                        license, url = '?', '?'
                     d['source_notice'] += f'\n{entry_point.dist.key} ({license}): {url}'
                     seen.add(entry_point.dist.key)