fix many module imports causing GC to pull the rug on our module instance

src/vm/wren_vm.c

@@ -446,10 +446,21 @@ static ObjClosure* compileInModule(WrenVM* vm, Value name, const char* source,
   {
     module = wrenNewModule(vm, AS_STRING(name));
 
+    // It's possible for the map set call below to resize the modules map,
+    // and trigger a GC while doing so. When this happens and there are enough
+    // objects and modules, it will collect the module we've just created.
+    // wrenPushRoot isn't an option when there are enough modules to exhaust
+    // WREN_MAX_TEMP_ROOTS, however handles are also not collected by GC.
+    // Note that this only affects the module until it's in the map, because
+    // then it has a reference to it, and won't be collected.
+    WrenHandle* moduleHandle = wrenMakeHandle(vm, OBJ_VAL(module));
+
     // Store it in the VM's module registry so we don't load the same module
     // multiple times.
     wrenMapSet(vm, vm->modules, name, OBJ_VAL(module));
 
+    wrenReleaseHandle(vm, moduleHandle);
+
     // Implicitly import the core module.
     ObjModule* coreModule = getModule(vm, NULL_VAL);
     for (int i = 0; i < coreModule->variables.count; i++)