[js] Make error friendly when isOrtFormat is undefined (#19958)

### Description
Make error friendly when isOrtFormat is undefined
(`onnxruntime.InferenceSession.create` is called with ArrayBuffer or
Uint8Array).

### Motivation and Context
I was trying to run my onnx model in WebGL EP, but it gave me the error
"Cannot read properties of null (reading 'irVersion')".
I used debugger to find that actual error is `int64 is not supported`,
but the error was invisible for me.
So I made it to show both error when isOrtFormat is undefined.
<s>I haven't written unit test yet, so I'm making it draft. (I have no
idea about how do I test this though...)</s>
[d62d942](d62d942)

js/web/lib/onnxjs/model.ts

@@ -16,6 +16,7 @@ export class Model {
   constructor() {}
 
   load(buf: Uint8Array, graphInitializer?: Graph.Initializer, isOrtFormat?: boolean): void {
+    let onnxError: Error|undefined;
     if (!isOrtFormat) {
       // isOrtFormat === false || isOrtFormat === undefined
       try {
@@ -25,10 +26,19 @@ export class Model {
         if (isOrtFormat !== undefined) {
           throw e;
         }
+        onnxError = e;
       }
     }
 
-    this.loadFromOrtFormat(buf, graphInitializer);
+    try {
+      this.loadFromOrtFormat(buf, graphInitializer);
+    } catch (e) {
+      if (isOrtFormat !== undefined) {
+        throw e;
+      }
+      // Tried both formats and failed (when isOrtFormat === undefined)
+      throw new Error(`Failed to load model as ONNX format: ${onnxError}\nas ORT format: ${e}`);
+    }
   }
 
   private loadFromOnnxFormat(buf: Uint8Array, graphInitializer?: Graph.Initializer): void {

js/web/test/e2e/browser-test-webgl.js

@@ -6,3 +6,16 @@
 it('Browser E2E testing - WebGL backend', async function() {
   await testFunction(ort, {executionProviders: ['webgl']});
 });
+
+it('Browser E2E testing - invalid buffer', async () => {
+  try {
+    await ort.InferenceSession.create(
+        new Uint8Array(Array.from({length: 100}, () => 42)), {executionProviders: ['webgl']});
+
+    // Should not reach here.
+    assert(false);
+  } catch (e) {
+    assert(e.message.includes('as ONNX format'));
+    assert(e.message.includes('as ORT format'));
+  }
+});