Properly detect failed signin because of invalid credentials in GC connector
Properly detect failed signin because of invalid credentials in GC connector

See https://github.com/cgeo/cgeo/issues/8818#issuecomment-696409866
The "Your password or username/email is incorrect" string is always there and dynamically added to the div
with id #signup-validation-error via client-side JS, under the condition that this div is present in the page.

Fixes #8818

matej116/cgeo,auricgoldfinger/cgeo,cgeo/cgeo,tobiasge/cgeo,cgeo/cgeo,S-Bartfast/cgeo,matej116/cgeo,matej116/cgeo,rsudev/c-geo-opensource,rsudev/c-geo-opensource,S-Bartfast/cgeo,cgeo/cgeo,rsudev/c-geo-opensource,S-Bartfast/cgeo,tobiasge/cgeo,auricgoldfinger/cgeo,cgeo/cgeo,auricgoldfinger/cgeo,tobiasge/cgeo