Fix Wasm2JS polyfill of Promise .catch() handler to work in WASM=2 mode (#11980)

* Fix Wasm2JS polyfill of Promise .catch() handler to work in WASM=2 mode

* Address review

src/wasm2js.js

@@ -77,7 +77,7 @@ WebAssembly = {
 #endif
           'instance': new WebAssembly.Instance(module)
         });
-#if ASSERTIONS
+#if ASSERTIONS || WASM == 2 // see postamble_minimal.js which uses .catch
         // Emulate a simple WebAssembly.instantiate(..).then(()=>{}).catch(()=>{}) syntax.
         return { catch: function() {} };
 #endif