glx/drisw: Nerf PutImage when loaderPrivate == NULL

This means the drawable was already destroyed. This can happen during
diplay teardown, destroying the context will make it current first so it
can flush rendering and destroy textures and such, and if the drawable
is already destroyed then flushing to nowhere would crash.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11423>

src/glx/drisw_glx.c

@@ -216,6 +216,9 @@ swrastPutImageShm(__DRIdrawable * draw, int op,
 {
    struct drisw_drawable *pdp = loaderPrivate;
 
+   if (!pdp)
+      return;
+
    pdp->shminfo.shmaddr = shmaddr;
    swrastXPutImage(draw, op, 0, 0, x, y, w, h, stride, shmid,
                    shmaddr + offset, loaderPrivate);
@@ -230,6 +233,9 @@ swrastPutImageShm2(__DRIdrawable * draw, int op,
 {
    struct drisw_drawable *pdp = loaderPrivate;
 
+   if (!pdp)
+      return;
+
    pdp->shminfo.shmaddr = shmaddr;
    swrastXPutImage(draw, op, x, 0, x, y, w, h, stride, shmid,
                    shmaddr + offset, loaderPrivate);
@@ -240,6 +246,9 @@ swrastPutImage2(__DRIdrawable * draw, int op,
                 int x, int y, int w, int h, int stride,
                 char *data, void *loaderPrivate)
 {
+   if (!loaderPrivate)
+      return;
+
    swrastXPutImage(draw, op, 0, 0, x, y, w, h, stride, -1,
                    data, loaderPrivate);
 }
@@ -249,6 +258,9 @@ swrastPutImage(__DRIdrawable * draw, int op,
                int x, int y, int w, int h,
                char *data, void *loaderPrivate)
 {
+   if (!loaderPrivate)
+      return;
+
    swrastXPutImage(draw, op, 0, 0, x, y, w, h, 0, -1,
                    data, loaderPrivate);
 }