Fix PROXY command bug

[AlexanderEpolite]

When PROXY is enabled, you can simply send:

PROXY IPV4 1.1.1.1

and the entire process will exit, with the error:

389 |                                         proxy: params[1].trim().toLowerCase()
390 |                                     },
391 |                                     '[%s] PROXY from %s through %s (%s)',
392 |                                     socketOptions.id,
393 |                                     params[1].trim().toLowerCase(),
394 |                                     params[2].trim().toLowerCase(),
                                                 ^
TypeError: undefined is not an object (evaluating 'params[2].trim')
      at socketReader (/mnt/c/Users/Alex/<private>/node_modules/smtp-server/lib/smtp-server.js:394:44)
      at emit (node:events:84:22)
      at emitReadable_ (internal:streams/readable:396:16)

This patch puts a try catch block around the problematic code, and returning an error to the sender if it is invalid.

The reason this happened in the first place is because params[2] was never checked to see if it was valid. Might be worth doing a manual check, but this does fix the issue.

Note: this is not too severe of a bug, as most people have proxy off, and the proxy would send correct data to begin with.