fix: in EXPORT_ALL and maybe other cases we export earlier than in maybeExport; just check if it exists already before exporting, don't override something

Author: kripken

src/modules.js

@@ -280,7 +280,10 @@ function maybeExport(name) {
   // stub with an error, so the user gets a message
   // if it is used, that they should export it
   if (ASSERTIONS) {
-    return 'Module["' + name + '"] = function() { abort("\'' + name + '\' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS.") };';
+    // check if it already exists, to support EXPORT_ALL and other cases
+    // (we could optimize this, but in ASSERTIONS mode code size doesn't
+    // matter anyhow)
+    return 'if (!Module["' + name + '"]) Module["' + name + '"] = function() { abort("\'' + name + '\' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS.") };';
   }
   return '';
 }