Fix fairygui memcpy leak

[MemoryTracker] ==== Memory Leaks (1) ====
[Leak] ptr=00000201C1A3CB40 size=16 thread=29652 type=NORMAL
  0>D:\dev\simdsoft\axmol3\axmol\platform\win32\MemoryTracker.h(368): ((uld::MemoryTracker::_on_alloc)+0xba)	00007FF6980717BA
  1>D:\dev\simdsoft\axmol3\axmol\platform\win32\MemoryTracker.h(195): ((uld::MemoryTracker::_hook_malloc_dbg)+0x66)	00007FF6980710A6
  2>C:\Program Files (x86)\Windows Kits\10\Source\10.0.26100.0\ucrt\heap\malloc.cpp(27): ((malloc)+0x1f)	0000000401070ACF
  3>D:\a\_work\1\s\src\vctools\crt\vcstartup\src\heap\new_scalar.cpp(36): ((operator new)+0x13)	00007FF699ECCFF3
  4>D:\a\_work\1\s\src\vctools\crt\vcstartup\src\heap\new_array.cpp(30): ((operator new[])+0x13)	00007FF699ECE0A3
  5>D:\dev\simdsoft\axmol3\extensions\fairygui\src\fairygui\UIPackage.cpp(18): ((fairygui::`dynamic initializer for 'emptyTextureData'')+0x10)	00007FF698039190
  6>C:\Program Files (x86)\Windows Kits\10\Source\10.0.26100.0\ucrt\startup\initterm.cpp(21): ((_initterm)+0x49)	00000004010B6A99
  7>D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl(258): ((__scrt_common_main_seh)+0x8b)	00007FF699ECDE2B
  8>D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl(331): ((__scrt_common_main)+0xe)	00007FF699ECDD8E
  9>D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_main.cpp(17): ((mainCRTStartup)+0xe)	00007FF699ECE07E
  10>((BaseThreadInitThunk)+0x17)	00007FFE2318E8D7
  11>((RtlUserThreadStart)+0x2c)	00007FFE2482C53C
[MemoryTracker] ==========================

Author: halx99

extensions/fairygui/src/fairygui/UIPackage.cpp

@@ -10,13 +10,11 @@ using namespace ax;
 
 using namespace std;
 
-const string UIPackage::URL_PREFIX = "ui://";
+const std::string UIPackage::URL_PREFIX = "ui://";
 int UIPackage::_constructing = 0;
 std::string UIPackage::_branch;
 std::unordered_map<std::string, std::string> UIPackage::_vars;
 
-const unsigned char* emptyTextureData = new unsigned char[16]{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
-
 std::unordered_map<std::string, UIPackage*> UIPackage::_packageInstById;
 std::unordered_map<std::string, UIPackage*> UIPackage::_packageInstByName;
 std::vector<UIPackage*> UIPackage::_packageList;
@@ -95,14 +93,8 @@ UIPackage* UIPackage::addPackage(const string& assetPath)
     if (it != _packageInstById.end())
         return it->second;
 
-    if (_emptyTexture == nullptr)
-    {
-        Image* emptyImage = new Image();
-        emptyImage->initWithRawData(emptyTextureData, 16, 2, 2, 4, false);
-        _emptyTexture = new Texture2D();
-        _emptyTexture->initWithImage(emptyImage);
-        delete emptyImage;
-    }
+    if (!_emptyTexture)
+        _emptyTexture = Director::getInstance()->getTextureCache()->getWhiteTexture();
 
     Data data;