[BUGFIX] Don't escape decimal character group

Resolves: #87471
Releases: master, 9.5, 8.7
Change-Id: I0d139369c5ddc3acd8acbd278fe9841961002ca0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62120

Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>

typo3/sysext/backend/Resources/Public/JavaScript/FormEngine.js

@@ -237,7 +237,7 @@ define(['jquery',
       // The incoming value consists of the table name, an underscore and the uid
       // or just the uid
       // For a single selection field we need only the uid, so we extract it
-      var pattern = /_(\\d+)$/
+      var pattern = /_(\d+)$/
         , result = value.toString().match(pattern);
 
       if (result != null) {