When a tab is created at startup (tabs restored from a previous session), we are not asked whether the password must be saved. The bug happens even if the page displayed in the tab is not the original page. In tabs open after startup, everything works.

I've spent quite a long time debugging this issue, I don't know much about how epiphany works, but here's what I've found:

- When "web_extension_page_created" is called for tabs open at startup, "web_extension" is NULL and the "page-created" signal is then not called (it's not NULL for other tabs).
- The "form-auth-data-save-requested" signal (responsible of showing the "do you want to store your password?" bar) is connected in "page_created_cb", so it's not connected for tabs open at startup.