[BUG] Subscribe Bookmarklet does not works twice

**Describe the bug**
if I use the bookmarklet twice on a page without saving, the second use is not the same

I mean this bookmarklet

**To Reproduce**
step 1
- go to a page with RSS (f.e. https://github.blog/)
- use the bookmarklet as usual
- the "add a RSS feed" page of FreshRSS apears
- 
- close this page (close the tab without clicking on submit and without cancel button)

step 2
- go back to the page of your interest from step 1
- use the bookmarklet again
- the "ass a RSS feed" page of FreshRSS apears again
- 
- but it did not recognize the RSS feed as the step before

**Expected behavior**
same result in step1 and step2

**Environment information (please complete the following information):**
- Browser: Firefox 88
- FreshRSS version: 1.18.0