[BUGFIX] Avoid endless loading of FormEngine

EditDocumentController failed to properly track if
the edit form could be created or not. This lead
to a couple of consequential errors. For example,
the spinner was added but could never be removed,
since the FormEngine JavaScript component was not
initialized.

With PHP > 8 this also lead to a lot of warnings
since $this->firstEl is not set, in case the edit
form could not be created.

This is now fixed by properly tracking whether the
edit form was created and whether $this->firstEl
was initialized. In case the edit form could not
be created, an info box notifies the user.

Resolves: #95183
Related: #95052
Releases: master
Change-Id: I5a710b22319f4ce34b86c64d2141b59ba3a7a12a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71023


Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/backend/Resources/Private/Language/locallang_alt_doc.xlf

@@ -42,6 +42,12 @@
 			<trans-unit id="noDocuments_listmodule" resname="noDocuments_listmodule">
 				<source>the Web&gt;List module</source>
 			</trans-unit>
+			<trans-unit id="noEditForm" resname="noEditForm">
+				<source>Edit form could not be loaded</source>
+			</trans-unit>
+			<trans-unit id="noEditForm.message" resname="noEditForm.message">
+				<source>The edit form could not be loaded for the requested records. This might be due to insufficient permissions.</source>
+			</trans-unit>
 			<trans-unit id="buttons.confirm.duplicate_record_changed.cancel" resname="buttons.confirm.duplicate_record_changed.cancel">
 				<source>Cancel</source>
 			</trans-unit>