Gracefully handle airodump crashing.

Apparently Airodump is capturing the SIGINT on some Ctrl+C presses.
Wifite will print out that airodump crashed w/ the return code & command executed.
Wifite will not change the list of targets if airodump crashes (to avoid wps:n/a).

py/Airodump.py

@@ -125,6 +125,7 @@ class Airodump(object):
 
     def get_targets(self, apply_filter=True):
         ''' Parses airodump's CSV file, returns list of Targets '''
+
         # Find the .CSV file
         csv_filename = None
         for fil in self.find_files(endswith='-01.csv'):
@@ -157,6 +158,9 @@ class Airodump(object):
                     # We decloaked a target!
                     self.decloaked_targets.append(new_target)
 
+        if self.pid.poll() is not None:
+            raise Exception('Airodump has stopped')
+
         self.targets = targets
         self.deauth_hidden_targets()