HTCPPurge() early exit on socket error

HTCPPurge() early exit on socket error

I tend to dislike code style such as:

	if( $ok ) {
		// lot of code
	} else {
		return false;
	}

The SquidUpdate::HTCPPurge() used that pattern to handle a
socket_create() issue.  I have simply moved the block above and inverted
the condition.  Ie:

	if( ! $ok ) {
		return false;
	}
	// lot of code

That saves a level of indentation and makes the code a bit easier to
follow IMHO.

Change-Id: Ic3c6e22bbb637352fef740a0c1663a4b6f5a2b6a