Update mqtt-publisher.py

Handle case of keys arg not provided

Author: mrbubble62

src/hal/user_comps/mqtt-publisher.py

@@ -116,6 +116,7 @@ def usage():
     @staticmethod
     def main():
         from optparse import Option, OptionParser
+        keys={}
         options = [
             Option( '--dryrun', dest='dryrun', action='store_true',
                     help='Dryrun, only collect HAL pin values, do not send them to MQTT.'),