IMAP emails without HTML content are shown as `false`

[i404788]

Describe the bug
Whenever an email is sent to the IMAP integration, shown in the team inbox & if the email only contains plain-text, then the shown body text is false

To Reproduce
Steps to reproduce the behavior:

1. Send plain-text email to IMAP integration
2. Restart integration (see IMAP doesn't refresh after initialization #249)
3. Observe false when opening the sent email

Expected behavior
The regular email body is shown

Screenshots
Plain-text:

HTML (<a href>)

Actual message:

Context (please include the related information if applicable):

• erxes version 1.2.3
• installation type docker