Fix calibre-debug -d broken by bug in smart_device_app

src/calibre/devices/smart_device_app/driver.py

@@ -351,6 +351,7 @@ def __init__(self, path):
         self.noop_counter = 0
         self.debug_start_time = time.time()
         self.debug_time = time.time()
+        self.is_connected = False
 
     def _debug(self, *args):
         # manual synchronization so we don't lose the calling method name