softgpu: Avoid over-aggressive rect conversion.

The TL and BR have to match between UVs and pos, not enough for UV to be
in order.  This was causing an artifact on Chains of Olympus' title.

GPU/Software/RasterizerRectangle.cpp

@@ -435,7 +435,9 @@ bool DetectRectangleFromFan(const RasterizerState &state, const VertexData *data
 
 			if (textl.x == texbl.x && textr.x == texbr.x && textl.y == textr.y && texbl.y == texbr.y) {
 				// Okay, the texture is also good, but let's avoid rotation issues.
-				return textl.y < texbr.y && textl.x < texbr.x;
+				const auto &postl = data[*tlIndex].screenpos;
+				const auto &posbr = data[*brIndex].screenpos;
+				return textl.y < texbr.y && postl.y < posbr.y && textl.x < texbr.x && postl.x < posbr.x;
 			}
 		}
 	}