repodb: Do not check compatibility if distro info is not included

Check distro name if specified in index file. If distro release is also
specified, check it for compatibility in addition to distro name.

pisi/db/repodb.py

@@ -247,10 +247,17 @@ class RepoDB(lazydb.LazyDB):
             return
 
         dist_name = self.get_distribution(name)
+        if dist_name is None:
+            return
+
+        compatible = dist_name == ctx.config.values.general.distribution
+
         dist_release = self.get_distribution_release(name)
+        if dist_release is not None:
+            compatible &= \
+                dist_release == ctx.config.values.general.distribution_release
 
-        if dist_name != ctx.config.values.general.distribution or \
-                dist_release != ctx.config.values.general.distribution_release:
+        if not compatible:
             self.deactivate_repo(name)
             raise IncompatibleRepoError(
                     _("Repository '%s' is not compatible with your "