Element Picker box does not spawn if no element filters exist

[Tykina]

Filter issues MUST NOT be reported here. Read first: https://github.com/gorhill/uBlock/blob/master/CONTRIBUTING.md

Describe the issue

The element picker / element zapper pop up box does not spawn (either from the popup menu, or from the context menu 'block element')

One or more specific URLs where the issue occurs

All

Screenshot in which the issue can be seen

n/a

Steps for anyone to reproduce the issue

(In Chromium or Vivaldi - I did not try other browsers)

1. Open the dashboard
2. Go to 'third party filters' and untick every subscription EXCEPT 'My Filters' - make sure 'Parse and enforce cosmetic filters' is ticked
3. Ensure 'My Filters' is empty (though in testing this, it does not need to be empty - it just needs to contain no cosmetic filters).
4. Visit any webpage, click uBlocks icon, click 'enter element picker mode' (alternatively right click a page and select 'Block Element' from the context menu)
5. The 'element picker' pop up never spawns

(as a workaround, if I ensure at least one cosmetic filter exists in 'My Filters', the pop up spawns correctly)

Your settings

[If you fail to provide this info, I will mark the issue as invalid. Lists all settings which differs from default settings]

• OS/version:

Windows 7 64 bit

• Browser/version:

Tested in

Vivaldi 1.13.1008.14 (Official Build) (32-bit)
Chromium 64.0.3259.0 (Official Build) (64-bit)

• uBlock Origin version:

1,14,19,2

Your filter lists

No subscribed filter lists

Your custom filters (if any)

In 'Third Party' filters, I have
|blob:$script

Under 'My Filters' I have
no-csp-reports: * true
* * 3p-frame block
* * 3p-script block

[gorhill]

Duplicate of #2963.