st/mesa: fix glCopyPixels(GL_STENCIL_INDEX) inverted position

If the renderbuffer orientation is Y=0=TOP we need to invert the dstY
position.

src/mesa/state_tracker/st_cb_drawpixels.c

@@ -865,6 +865,10 @@ copy_stencil_pixels(GLcontext *ctx, GLint srcx, GLint srcy,
       usage = PIPE_TRANSFER_READ_WRITE;
    else
       usage = PIPE_TRANSFER_WRITE;
+   
+   if (st_fb_orientation(ctx->DrawBuffer) == Y_0_TOP) {
+      dsty = rbDraw->Base.Height - dsty - height;
+   }
 
    ptDraw = st_cond_flush_get_tex_transfer(st_context(ctx),
 					   rbDraw->texture, 0, 0, 0,