Fix MD2 rollangle in reverse gravity

src/hardware/hw_md2.c

@@ -1478,7 +1478,7 @@ boolean HWR_DrawModel(gr_vissprite_t *spr)
 
 			// rotation pivot
 			p.centerx = FIXED_TO_FLOAT(spr->mobj->radius/2);
-			p.centery = FIXED_TO_FLOAT(spr->mobj->height/2);
+			p.centery = FIXED_TO_FLOAT(spr->mobj->height/(flip ? -2 : 2));
 
 			// rotation axis
 			if (sprinfo->available)
@@ -1490,6 +1490,9 @@ boolean HWR_DrawModel(gr_vissprite_t *spr)
 				p.rollflip = 1;
 			else if ((sprframe->rotate & SRF_LEFT) && (ang >= ANGLE_180)) // See from left
 				p.rollflip = -1;
+
+			if (flip)
+				p.rollflip *= -1;
 		}
 
 		p.anglex = 0.0f;