fix: repair two broken error paths in the sender

[andris9]

Two correctness fixes in the sender's error-handling paths, both found during review of #497.

1. Unexpected-close handler discarded its own error object

The setTimeout that fires on an unexpected clean connection close builds a synthetic error (category: 'network', temporary: true) but then called handleError(delivery, connection, err) — passing err, the getConnectionWithCache callback param, which is guaranteed falsy past its own if (err) return guard. So `Network error: ${err.message}` threw a TypeError inside an unref()'d timer instead of deferring the delivery. The constructed error was never used. Broken since #363 (Jan 2024).

Fix: pass the constructed error and read error.message.

2. has-a-code guard tested the raw response, not the normalized one

In handleResponseError, the "does this carry an SMTP code" guard tested the raw string with /^\d{3}\b/, while bounces.check() classifies the normalized string (formatSMTPResponse trims a leading CRLF/space ahead of the code). A 5xx arriving with leading whitespace — e.g. a cache-restored response, where responseCode is not restored — failed the raw test, fell into the network-defer branch, and deferred forever instead of rejecting.

Fix: hoist the smtpResponse normalization (already computed ~15 lines lower for logging) above the branch and test that, so the guard and the classifier consume the same string. Net −1 line; removes a duplicate formatSMTPResponse call.

Verified

• Reproduced Modify message and send to specify server #1: the old binding throws TypeError: Cannot read properties of null (reading 'message'); the fix builds the error and routes it as a network defer through the real handleResponseError.
• Drove the real handleResponseError for TypeScript #2 with the cache-restore shape (response set, no responseCode): \r\n550 ... now rejects and \r\n554 ... not allowed to connect now defers+blacklists, where both previously deferred forever. Non-whitespace cases unchanged.
• New bounces-test.js cases lock in the load-bearing property (formatSMTPResponse strips leading CRLF/space) that the guard now depends on. Suite + eslint green.

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