fixed an issue with zIndexing (#748)

zIndexMin and zIndexMax were not updated in time. Causing issues when
setting.

Author: wouterlucas

src/core/CoreNode.ts

@@ -1893,8 +1893,6 @@ export class CoreNode extends EventEmitter {
     const inRttCluster =
       this.props.rtt === true || this.parentHasRenderTexture === true;
     const children = this.children;
-    const min = this.zIndexMin;
-    const max = this.zIndexMax;
     const zIndex = node.zIndex;
     const autosizeTarget = this.autosizer || this.parentAutosizer;
     let attachToAutosizer = autosizeTarget !== null;
@@ -1932,7 +1930,14 @@ export class CoreNode extends EventEmitter {
 
     children.push(node);
 
-    if (min !== max || (zIndex !== min && zIndex !== max)) {
+    if (zIndex < this.zIndexMin) {
+      this.zIndexMin = zIndex;
+    }
+    if (zIndex > this.zIndexMax) {
+      this.zIndexMax = zIndex;
+    }
+
+    if (this.zIndexMax !== this.zIndexMin) {
       this.zIndexSortList.push(node);
       this.setUpdateType(UpdateType.SortZIndexChildren);
     }

src/core/lib/collectionUtils.ts

@@ -73,11 +73,12 @@ export const incrementalRepositionByZIndex = (
 
     //binary search for correct insertion position
     let left = 0;
-    let right = nodes.length;
+    let right = currentIndex === nodes.length - 1 ? currentIndex : nodes.length;
 
     while (left < right) {
       const mid = (left + right) >>> 1;
-      if (nodes[mid]!.props.zIndex <= targetZIndex) {
+      const target = nodes[mid]!;
+      if (target.props.zIndex <= targetZIndex) {
         left = mid + 1;
       } else {
         right = mid;