[embind] Fix closure with assertions enabled. (emscripten-core#22760)

`argPackAdvance` was being minified so the check for the property was
not working when assertions were enabled with closure.

Fixes emscripten-core#22759

Author: brendandahl

src/embind/embind.js

@@ -266,7 +266,7 @@ var LibraryEmbind = {
   $registerType__docs: '/** @param {Object=} options */',
   $registerType: function(rawType, registeredInstance, options = {}) {
 #if ASSERTIONS
-    if (!('argPackAdvance' in registeredInstance)) {
+    if (registeredInstance.argPackAdvance === undefined) {
       throw new TypeError('registerType registeredInstance requires argPackAdvance');
     }
 #endif

test/test_other.py

@@ -3234,7 +3234,7 @@ def test_embind_closure_no_dynamic_execution(self):
     'o1': ['-O1'],
     'o2': ['-O2'],
     'o2_mem_growth': ['-O2', '-sALLOW_MEMORY_GROWTH', test_file('embind/isMemoryGrowthEnabled=true.cpp')],
-    'o2_closure': ['-O2', '--closure=1', '--closure-args', '--externs ' + shlex.quote(test_file('embind/underscore-externs.js'))],
+    'o2_closure': ['-O2', '--closure=1', '--closure-args', '--externs ' + shlex.quote(test_file('embind/underscore-externs.js')), '-sASSERTIONS=1'],
     'strict_js': ['-sSTRICT_JS']
   })
   def test_embind(self, *extra_args):