Fix PC sprite left-edge clipping underwrite

[segrax]

Motivation

• Prevent a heap-buffer underwrite in the PC renderer where left-edge clipping could leave mVideo_Draw_PosX negative and cause Video_Draw_8 to write before the row/buffer start.

Description

• Add a post-clip guard in cGraphics_PC::Sprite_OnScreen_Check (Source/PC/Graphics_PC.cpp) that advances mVideo_Draw_PosX to non-negative and reduces mVideo_Draw_Columns when left-edge clipping would otherwise leave PosX < 0.

Testing

• No automated unit tests were run against the patched code in this environment; a full build with SDL headers was not possible here.

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Codex Task