compatible with non-compliant responses with excessive SPACE

[qjebbs]

This PR improves compatibility with non-compliant servers, by skipping excessive SPACE between elements and the trailing SPACE

• imap.exmail.qq.com: * CAPABILITY IMAP4<SP>IMAP4rev1<SP><CRLF>
• smtp-n.global-mail.cn: * SEARCH<SP><CRLF>

related: #571 #540

[qjebbs]

the second commit skip all potential excessive SPACEs tries to solve all similar problems as it suggests, but I am not sure if I do it in the right way.

[qjebbs]

It works good in my env, the only question that comes to mind is whether SP(), ExpectSP() needs to be renamed (e.g.: LSP() for leading Space) for method semantics reasons.

[qjebbs]

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