Only run final command if one is set

pronterface.py

@@ -192,8 +192,10 @@ class PronterWindow(wx.Frame,pronsole.pronsole):
             wx.CallAfter(self.pausebtn.Disable)
             wx.CallAfter(self.printbtn.SetLabel,_("Print"))
 
-            import shlex
             param = self.settings.final_command
+            if not param:
+                return
+            import shlex
             pararray=[i.replace("$s",str(self.filename)).replace("$t", format_time(int(time.time()-self.starttime+self.extra_print_time))).encode() for i in shlex.split(param.replace("\\","\\\\").encode())]
             self.finalp=subprocess.Popen(pararray,stderr=subprocess.STDOUT,stdout=subprocess.PIPE)