osinstall: Fix m1n1 installation

When installing m1n1, no package needs to be downloaded and the URL
cache is None, triggering an exception when close_connection is
called on it.

Signed-off-by: Javier Alvarez <[email protected]>

Author: Javier-varez

src/osinstall.py

@@ -120,7 +120,8 @@ def install(self, stub_ins):
         logging.info("OSInstaller.install()")
 
         # Force a reconnect, since the connection is likely to have timed out
-        self.ucache.close_connection()
+        if self.ucache is not None:
+            self.ucache.close_connection()
 
         icon = self.template.get("icon", None)
         if icon: