console: fix error with old pygobject

The code doesn't work as expected. From python documentation:

    x and y

is the same as

    x if not x or y

so in the code if for some reasone `dev` is None the value stored in
`sensitive` will be None as well.

No the code itself works with pygobject >= 3.31.3 where they allowed
None as a valid boolean value, but with older versions it will fail
with this error message:

    TypeError: Argument 1 does not allow None as a value

Resolves: https://github.com/virt-manager/virt-manager/issues/226

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>

virtManager/details/console.py

@@ -258,7 +258,7 @@ class _ConsoleMenu:
 
             cb = toggled_cb
             cbdata = dev
-            sensitive = dev and not tooltip
+            sensitive = bool(dev and not tooltip)
 
             active = False
             if oldlabel is None and sensitive: