Message parsing is not working as expected.

[rosehgal]

Describe the bug
Message parsing is not working as expected. If you send a very basic HTML mail from any mail service. Following parameters a coming out to be true.

MailParser    : Is plain content true
MailParser    : Is HTML content true
MailParser    : Is multipart true
MailParser    : Is plain content Empty false

Due to which, this statement is never reached. https://github.com/r0hi7/Trashemail/blob/b67de8bfface2386071b32b9a9930d90a77d8b20/src/main/java/io/github/trashemail/utils/MailParser.java#L39
Because this is evaluated to false: https://github.com/r0hi7/Trashemail/blob/b67de8bfface2386071b32b9a9930d90a77d8b20/src/main/java/io/github/trashemail/utils/MailParser.java#L38

To Reproduce
Steps to reproduce the behavior:

1. Send an HTML mail from good with the following content.

**Bold text**
_Italic_

Expected behavior
Since this is multipart mail, the HTML field should be processed. And HTML message should be recorded.

[rosehgal]

@nishitm, I am checking on this. But since, you merged the PR for this, can you cross verify this issue?

[rosehgal]

The RC of this bug was that it was not ever checking for multipart data.

[rosehgal]

Fixed in #26