glx: Don't destroy context with XID 0

We use XID 0 to indicate the context has already been destroyed, but it's
currently bound.

src/glx/dri2_glx.c

@@ -119,7 +119,8 @@ dri2_destroy_context(__GLXcontext *context)
    struct dri2_context *pcp = (struct dri2_context *) context;
    struct dri2_screen *psc = (struct dri2_screen *) context->psc;
 
-   glx_send_destroy_context(psc->base.dpy, context->xid);
+   if (context->xid)
+      glx_send_destroy_context(psc->base.dpy, context->xid);
 
    if (context->extensions)
       XFree((char *) context->extensions);

src/glx/dri_glx.c

@@ -505,7 +505,8 @@ dri_destroy_context(__GLXcontext * context)
    struct dri_context *pcp = (struct dri_context *) context;
    struct dri_screen *psc = (struct dri_screen *) context->psc;
 
-   glx_send_destroy_context(psc->base.dpy, context->xid);
+   if (context->xid)
+      glx_send_destroy_context(psc->base.dpy, context->xid);
 
    if (context->extensions)
       XFree((char *) context->extensions);

src/glx/drisw_glx.c

@@ -245,7 +245,8 @@ drisw_destroy_context(__GLXcontext *context)
    struct drisw_context *pcp = (struct drisw_context *) context;
    struct drisw_screen *psc = (struct drisw_screen *) context->psc;
 
-   glx_send_destroy_context(psc->base.dpy, context->xid);
+   if (context->xid)
+      glx_send_destroy_context(psc->base.dpy, context->xid);
 
    if (context->extensions)
       XFree((char *) context->extensions);

src/glx/glxcmds.c

@@ -584,7 +584,7 @@ glx_send_destroy_context(Display *dpy, XID xid)
 static void
 indirect_destroy_context(__GLXcontext *gc)
 {
-   if (!gc->imported)
+   if (!gc->imported && gc->xid)
       glx_send_destroy_context(gc->psc->dpy, gc->xid);
 
    __glXFreeVertexArrayState(gc);
@@ -619,6 +619,8 @@ DestroyContext(Display * dpy, GLXContext gc)
        * Note that we set gc->xid = None above.  In MakeContextCurrent()
        * we check for that and delete the context there.
        */
+      if (!gc->imported)
+	 glx_send_destroy_context(dpy, gc->xid);
       gc->xid = None;
       __glXUnlock();
       return;