Link field bug on none existing node reference

Thanks @msq for reporting this bug and also creating a patch for it.

I did replicated the issue as mentioned and just wanna share that point "Saving node A will result in 404 response" is not true, node is saved as expected but yes reference to deleted node still persist in the article which may result in 404 when viewing the article from user experience point of view.

I also applied patch for the same and confirm that patch is applied successfully with no issues and upon resaving or opening the article content i can see that "" is used to deleted content and also it is not visible in the frontend side.

Attaching screenshot for reference above mentioned points and changing status to needs review, so this issue can move forward with closure.

As a bug will need a test case to show the issue.

Updated the issue summary as per commet #3

Moving to needs review for #8

Please update MR to 11.x