[FIX] hw_escpos: do not start queue processor if ESC/POS not available

bzr revid: odo@openerp.com-20140218110824-pdy54bdmm0appntu

addons/hw_escpos/controllers/main.py

@@ -95,6 +95,9 @@ class EscposDriver(Thread):
             _logger.warning('ESC/POS Device Disconnected: '+message)
 
     def run(self):
+        if not escpos:
+            _logger.error('ESC/POS cannot initialize, please verify system dependencies.')
+            return
         self.queue = Queue()
         while True:
             try: