Fix dedupe screen to always set the checkbox to 'ticked' where data w…

…ould otherwise be lost

Full details are here civicrm#15595 - although this does not include the
cleanup commits I did getting to this point.

Bug: T235450
Change-Id: I60d93df0ee3d34ff5c3b7b7c7e5034aafbdfd740

CRM/Contact/Form/Merge.php

@@ -225,13 +225,16 @@ public function preProcess() {
           // @todo consider enabling if it is an add & defaulting to true.
           $element[4] = array_merge((array) CRM_Utils_Array::value(4, $element, []), ['disabled' => TRUE]);
         }
-        $this->addElement($element[0],
+        $newCheckBox = $this->addElement($element[0],
           $element[1],
           array_key_exists('2', $element) ? $element[2] : NULL,
           array_key_exists('3', $element) ? $element[3] : NULL,
           array_key_exists('4', $element) ? $element[4] : NULL,
           array_key_exists('5', $element) ? $element[5] : NULL
         );
+        if (!empty($element['is_checked'])) {
+          $newCheckBox->setChecked(TRUE);
+        }
       }
 
       // add related table elements

CRM/Dedupe/Merger.php

@@ -1138,12 +1138,13 @@ public static function getRowsElementsAndInfo($mainId, $otherId, $checkPermissio
           // Display a checkbox to migrate, only if the values are different
           if ($value != $main[$field]) {
             $elements[] = [
-              'advcheckbox',
-              "move_$field",
-              NULL,
-              NULL,
-              NULL,
-              $value,
+              0 => 'advcheckbox',
+              1 => "move_$field",
+              2 => NULL,
+              3 => NULL,
+              4 => NULL,
+              5 => $value,
+              'is_checked' => (!isset($main[$field]) || $main[$field] === ''),
             ];
           }