end() on pg.Client hangs if connect() fails

[MasterOdin]

Given the following code:

const pg = require('pg');
const client = new pg.Client({ host: 'bogushost' });
try {
  await client.connect();
} catch (err) {
  // pass
}
await client.end();

The end() call will hang indefinitely. I've seen this happen with at least ENOTFOUND and ECONNREFUSED errors.

[MasterOdin]

Slightly different case than #2716, but it ends up the same root cause where the underlying client.connection.stream issues end when the connection fails, and so calling client.end hangs as the end event has already fired. The fix in #2717 fixes this bug as it adds a flag around detecting if the end event was fired. 👍