Blocked Frames have no Placeholder nor display <noframes> #120

Prerequisites

• I performed a cursory search of the issue tracker to avoid opening a duplicate issue
  • Your issue may already be reported.
  • I also searched the existing issues at https://github.com/gorhill/uMatrix/issues
• This is not a support issue or a question
  • Support issues and questions are handled at /r/uMatrix
• I tried to reproduce the issue when...
  • uMatrix is the only extension
  • uMatrix with default lists/settings
  • using a new, unmodified browser profile
• I am running the latest version of uMatrix
• I checked the documentation to understand that the issue I report is not a normal behavior
• I used the logger to rule out that the issue is caused by my ruleset

Description

Blocked iframes get replaced with a placeholder, but blocked frames (in a frameset) just display a white page. The (obsolete) <noframes> element is not displayed either, even if 1st-party-frames are blocked too.

A specific URL where the issue occurs

http://spth.de/

Steps to Reproduce

1. make sure some frames are blocked
2. navigate to a website that uses frames, e.g. http://spth.de (uses 3rd party frame)
3. instead of a placeholder, nothing is displayed

Ruleset

https-strict: behind-the-scene false
matrix-off: about-scheme true
matrix-off: behind-the-scene true
matrix-off: chrome-extension-scheme true
matrix-off: chrome-scheme true
matrix-off: moz-extension-scheme true
matrix-off: opera-scheme true
matrix-off: vivaldi-scheme true
matrix-off: wyciwyg-scheme true
noscript-spoof: * true
referrer-spoof: * true
referrer-spoof: behind-the-scene false
* * * block
* * css allow
* * frame block
* * image allow
* 1st-party * allow
* 1st-party frame allow

Supporting evidence

https://imgur.com/6ekhiRG.png

Your environment

• uMatrix version: 1.3.16
• Browser Name and version: firefox-65.0.2-1.fc29.x86_64
• Operating System and version: PRETTY_NAME="Fedora 29 (Twenty Nine)"