Catch exception that occurs when stopping a web app that has not started (fixes #237)

onionshare/web.py

@@ -279,6 +279,7 @@ def stop(port):
     Stop the flask web server by loading /shutdown.
     """
     # to stop flask, load http://127.0.0.1:<port>/<shutdown_slug>/shutdown
+    try:
         if transparent_torification:
             import socket
 
@@ -287,3 +288,5 @@ def stop(port):
             s.sendall('GET /{0:s}/shutdown HTTP/1.1\r\n\r\n'.format(shutdown_slug))
         else:
             urllib2.urlopen('http://127.0.0.1:{0:d}/{1:s}/shutdown'.format(port, shutdown_slug)).read()
+    except:
+        pass