Read all part content use ReadPartErrorPolicy.

[ly020044]

Hi,

The ReadPartErrorPolicy only used by content type text/*, Wouldn't it be better to use ReadPartErrorPolicy to control known errors when reading all part content?

For example, if the content type is image/*, a base64.CorruptInputError occurs while reading part content. This image may also be displayed if this error is ignored.

[iredmail]

This PR can be used to fix errors like [E] Malformed Base64: illegal base64 data at input byte 0.

We already processed many emails with this error, the cause is base64 encoded attachment (e.g. image) is incomplete.

If we open this email with MUA like Thunderbird or macOS Mail.app, email body is fine, but the image is partly rendered (we can still view part of the image).

With this PR, we can define a policy like existing AllowCorruptTextPartErrorPolicy (but for all content types) to ignore base64 corrupt input, then successfully parse the email and get the incomplete image (which is expected).

[iredmail]

hi @jhillyerd,

Could you help review this PR and hopefully merge it?