fix PX_Initialize bug

[dududuguo]

Fix #119

Fix SEGV crash when screen size is too small

When screen dimensions are less than 25x25, PX_Object_ScrollAreaCreate() returns PX_NULL, but PainterEngine_Initialize() did not properly handle this case and continued execution with an uninitialized memory pool pointer (mp). This led to a SEGV crash when the null pointer was later dereferenced.

by:

1. Adding null pointer check for mp in PX_Object_FireworkKICreate()
2. Initializing mp to NULL in PainterEngine_Initialize()
3. Adding proper error handling when mp initialization fails:
   • Add error messages for failed memory pool initialization
   • Add message indicating minimum window size requirement (24x24)
   • Return PX_FALSE to prevent further execution with invalid mp