Codechange: address CodeQL issue "Multiplication result converted to larger type" (#10306)

Most are very unlikely to ever be triggered in our codebase; two
stand out: linkgraph and money cheat. Those, potentially, could
wrap earlier than expected.

src/blitter/32bpp_base.cpp

@@ -140,9 +140,9 @@ void Blitter_32bppBase::ScrollBuffer(void *video, int &left, int &top, int &widt
 	}
 }
 
-int Blitter_32bppBase::BufferSize(int width, int height)
+size_t Blitter_32bppBase::BufferSize(uint width, uint height)
 {
-	return width * height * sizeof(uint32);
+	return sizeof(uint32) * width * height;
 }
 
 void Blitter_32bppBase::PaletteAnimate(const Palette &palette)