Image-only emails fail to send

Creating an html email with just an image (ie a poster) and trying to send a test results in a misleading error in the UI:

Could not identify any recipients. Perhaps the group is empty?

The logs however record the correct warning:

CiviMail will not send an empty mail body, Skipping: some@email.com

The mailing can still be scheduled and is sent, but no deliveries are made; the report claims X intended recipients, 0 deliveries, 0 bounces.

This seems to happen for any mailing with no apparent text. Exaple:

<html>
<body>
<img src="https://civicrm.org/sites/all/themes/civicrm_bootstrap/logo.png">
</body>
</html>

Given that sending an image-only email with no plain text version is bad practice, it can be argued that this is a feature and not a bug but if that's the case, a clearer UI error is needed.