Emscripten: Only call DumpTraceback if it exists (#160305)

Prevents an error-inside-of-error situation. Since we know that something has
gone wrong already, the runtime might be in a bad state.

Author: hoodmane

Platforms/emscripten/node_entry.mjs

@@ -57,6 +57,11 @@ try {
   // Show JavaScript exception and traceback
   console.warn(e);
   // Show Python exception and traceback
-  Module.PyUnstable_DumpTraceback(2, Module._PyGILState_GetThisThreadState());
+  try {
+    Module.PyUnstable_DumpTraceback?.(2, Module._PyGILState_GetThisThreadState());
+  } catch(e) {
+    console.warn("Error occurred while attempting to format a Python traceback:");
+    console.warn(e);
+  }
   process.exit(1);
 }