Fix shader emission for NME (#17010)

Co-authored-by: David Catuhe <[email protected]>

Author: deltakosh

packages/dev/core/src/Materials/Node/nodeMaterial.ts

@@ -1038,8 +1038,8 @@ export class NodeMaterial extends PushMaterial {
 
         this._buildIsInProgress = false;
         if (noError) {
-            this.onBuildObservable.notifyObservers(this);
             this._buildWasSuccessful = true;
+            this.onBuildObservable.notifyObservers(this);
         }
 
         // Wipe defines

packages/tools/nodeEditor/src/components/propertyTab/propertyTabComponent.tsx

@@ -586,7 +586,9 @@ export class PropertyTabComponent extends React.Component<IPropertyTabComponentP
                         label="Export shaders"
                         onClick={() => {
                             this.props.globalState.nodeMaterial.build();
-                            StringTools.DownloadAsFile(this.props.globalState.hostDocument, this.props.globalState.nodeMaterial.compiledShaders, "shaders.txt");
+                            this.props.globalState.nodeMaterial.onBuildObservable.addOnce(() => {
+                                StringTools.DownloadAsFile(this.props.globalState.hostDocument, this.props.globalState.nodeMaterial.compiledShaders, "shaders.txt");
+                            });
                         }}
                     />
                     {this.props.globalState.customSave && (