pipe-loader: destroy sw_winsys on sw_release

The sw pipe-loader implicitly handles winsys_create, thus we
it would make sense to implicitly destroy it upon releasing
the loader.

Currently we leak the sw_winsys when releasing the pipe-loader.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>

src/gallium/auxiliary/pipe-loader/pipe_loader_sw.c

@@ -75,6 +75,9 @@ pipe_loader_sw_release(struct pipe_loader_device **dev)
 {
    struct pipe_loader_sw_device *sdev = pipe_loader_sw_device(*dev);
 
+   if (sdev->ws && sdev->ws->destroy)
+      sdev->ws->destroy(sdev->ws);
+
    if (sdev->lib)
       util_dl_close(sdev->lib);