coverity: FORWARD_NULL correct

pywbem/cim_obj.py:1843: assign_undefined: Assigning: "kb_assigns" = "undefined".
pywbem/cim_obj.py:1957: property_access: Accessing a property of null-like value "kb_assigns".

Ensure the variable exists and is initialized as a list.

Signed-off-by: Tony Asleson <tasleson@redhat.com>

pywbem/_cim_obj.py

@@ -2052,6 +2052,7 @@ def from_wbem_uri(wbem_uri):
                 _format("WBEM URI has an invalid format for its keybindings: "
                         "{0!A}", keybindings_str))
 
+        kb_assigns = []
         if m.group(1):
             kb_assigns = [m.group(1)]