fix: harden mipmap creation failure handling

[luojiyin1987]

Summary

• Create scaled GDI bitmaps in _viv_create_mipmap_bitmap.
• Keep GDI resource handling out of _viv_get_mipmap.
• Publish each mipmap only after bitmap creation succeeds.
• Free partial resources and return the last valid mipmap after failure.
• Capture each GDI error before cleanup changes the thread error state.

Validation

• git diff --check
• Reviewed each GDI failure path for cleanup and fallback behavior.
• A full build needs the Windows MSVC environment.