Add null check for config when clicking on wifi picker entry

Null check is needed when getting wifi configuration instead of relying
on isSaved() since isSaved() may be true while getWifiConfiguration() is
null.

Bug: 153029289
Test: manual tapping on suggested entry and verifying no crash
Change-Id: Id487f48bd2079d596ea157920e4709fb8407ee9f
1 file changed