SINGLE_FILE + ASSERTIONS fix (#5680)

Author: buu700

src/jsifier.js

@@ -522,6 +522,8 @@ function JSify(data, functionsOnly) {
       print('assert(STACK_MAX < SPLIT_MEMORY, "SPLIT_MEMORY size must be big enough so the entire static memory + stack can fit in one chunk, need " + STACK_MAX);\n');
     }
 
+    if (ASSERTIONS) print('var ASSERTIONS = true;\n');
+
     print(preprocess(read('arrayUtils.js')));
     // Export all arrayUtils.js functions
     print(maybeExport('intArrayFromString'));
@@ -551,8 +553,6 @@ function JSify(data, functionsOnly) {
     // "Final shape that will be created").
     print('// EMSCRIPTEN_END_FUNCS\n');
 
-    if (ASSERTIONS) print('var ASSERTIONS = true;\n');
-
     if (HEADLESS) {
       print('if (!ENVIRONMENT_IS_WEB) {');
       print(read('headlessCanvas.js'));