Fix Amiga sprite left-clip negative X underwrite

[segrax]

Motivation

• Prevent negative sprite X positions from surviving left-edge clipping in the Amiga renderer and causing an out-of-bounds write in Video_Draw_8 when mVideo_Draw_PosX can be -1.

Description

• Add a post-left-clip safety check in cGraphics_Amiga::Sprite_OnScreen_Check(bool) that returns false if mVideo_Draw_PosX < 0, implemented as a minimal three-line change in Source/Amiga/Graphics_Amiga.cpp to reject sprites that would underwrite the surface buffer.

Testing

• No full automated test suite was executed due to missing SDL development headers in the environment, and the change was verified via source-level checks (git diff and nl -ba) which confirmed the intended insertions.

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Codex Task