Can't turn on viewing emails in plain text

[w201403]

Please search to check for an existing issue (including closed issues, for which the fix may not have yet been released) before opening a new issue: https://github.com/k9mail/k-9/issues?q=is%3Aissue

Expected behavior

Tell us what should happen

Actual behavior

Tell us what happens instead

Steps to reproduce

Environment

K-9 Mail version:

Android version:

Account type (IMAP, POP3, WebDAV/Exchange):

[cketti]

See #906