remove some UB

- savestates used to read a four bytes from a single byte value
- a few unassigned variables
- some other things
- also make the ROR macro an inline function

src/GPU2D.cpp

@@ -102,6 +102,7 @@ GPU2D::~GPU2D()
 
 void GPU2D::Reset()
 {
+    Enabled = false;
     DispCnt = 0;
     memset(BGCnt, 0, 4*2);
     memset(BGXPos, 0, 4*2);