make Director::end() reantrant

cocos2dx/CCDirector.cpp

@@ -704,8 +704,11 @@ void Director::purgeDirector()
     CHECK_GL_ERROR_DEBUG();
     
     // OpenGL view
+    if (_openGLView)
+    {
         _openGLView->end();
         _openGLView = nullptr;
+    }
 
     // delete Director
     release();

cocos2dx/kazmath/src/GL/mat4stack.c

@@ -66,8 +66,14 @@ void km_mat4_stack_pop(km_mat4_stack* stack, kmMat4* pOut)
     stack->top = &stack->stack[stack->item_count - 1];
 }
 
-void km_mat4_stack_release(km_mat4_stack* stack) {
+void km_mat4_stack_release(km_mat4_stack* stack)
+{
+    if (stack->stack)
+    {
         free(stack->stack);
+        stack->stack = NULL;
+    }
+    
     stack->top = NULL;
     stack->item_count = 0;
     stack->capacity = 0;

cocos2dx/support/user_default/CCUserDefault.mm

@@ -503,6 +503,7 @@ UserDefault* UserDefault::getInstance()
 
 void UserDefault::destroyInstance()
 {
+    delete _userDefault;
     _userDefault = NULL;
 }
 

cocos2dx/textures/CCTextureCache.cpp

@@ -88,6 +88,8 @@ TextureCache::~TextureCache()
 }
 
 void TextureCache::destroyInstance()
+{
+    if (_sharedTextureCache)
     {
         // notify sub thread to quick
         _sharedTextureCache->_needQuit = true;
@@ -96,6 +98,7 @@ void TextureCache::destroyInstance()
         
         CC_SAFE_RELEASE_NULL(_sharedTextureCache);
     }
+}
 
 const char* TextureCache::description() const
 {