wpaspy: Fix potentially referencing non existing attribute

wpaspy: Fix potentially referencing non existing attribute

In wpaspy.py in the Ctrl object constructor there is a try/except. In
the except part the code references the s attribute of the object. This
attribute is only created later in the try part. If an exception occurs
before the attribute creation then the except part references a non
existing attribute. Fix that by assigning None to the s attribute at the
beginning of the try part.

Signed-off-by: Jonathan Afek <jonathanx.afek@intel.com>