prefer-plain: Runtime warnings for "Only ever show plain text"
Having set "Only ever show plain text" for the prefer-plain and viewing a message, which has only text/html part and which contains references to remote content (https://....
), there are printed runtime warnings like:
e_web_view_process_uri_request: Cannot find handler for scheme 'evo-https'
That's because the prefer-plain loads the HTML data into a temporary EWebView, to convert it to the plain text, but the EWebView recognizes remote URLs and want to handle them, but there's no handler registered, thus it claims a problem on the terminal.
This patch adds a "null" scheme handler, which always errors out, in the prefer-plain for the schemes the EMailDisplay
uses.