If server-string can't be parsed, fall back to localhost.

Co-Authored-By: ghost43 <somber.night@protonmail.com>

electrum/network.py

@@ -268,8 +268,8 @@ class Network(Logger):
             try:
                 deserialize_server(self.default_server)
             except:
-                print('Failed to parse server-string.')
+                self.logger.warning('failed to parse server-string; falling back to localhost.')
-                exit()
+                self.default_server = "localhost:50002:s"
         if not self.default_server:
             self.default_server = pick_random_server()