Allow switching property editor from numeric to slider (#11287)

* Make it possible to change from numeric/decimal property editor to slider without breaking editor

* Formatting

src/Umbraco.Web.UI.Client/src/views/propertyeditors/slider/slider.controller.js

@@ -45,8 +45,13 @@
         if (!$scope.model.value) {
             $scope.model.value = start.toString();
         }
-        // convert to array
-        $scope.sliderValue = $scope.model.value ? $scope.model.value.split(',') : null;
+
+        // convert to array - exiting value can be a number if switching from numeric/decimal property editor
+        $scope.sliderValue = $scope.model.value
+            ? Utilities.isString($scope.model.value) || Utilities.isNumber($scope.model.value)
+                    ? $scope.model.value.toString().split(',')
+                    : null
+            : null;
         
         // don't render values with decimal places if the step increment in a whole number
         var stepDecimalPlaces = $scope.model.config.step % 1 == 0