cli: connect after verifying args, not before

[iancoleman]

To reproduce

safe files download <address>

Tries to connect (takes about 10s, quite a long time)

Shows error unrelated to network connection:

Error: 
   0: Both the name and address must be supplied if either are used

This error could be shown before connecting to the network.

It's a better ux to fail fast. It's less network load to avoid connection if it won't be used.

Main place to look at is sn_cli/src/main.rs L85-108

There's a similar ux concern with wallet commands, eg address and receive, which don't need a connection but will establish one anyway.