glthread: fix restoring the dispatch in destroy when the context is not current

also remove an invalid comment in mtypes.h

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14000>

src/mesa/main/glthread.c

@@ -176,15 +176,10 @@ _mesa_glthread_destroy(struct gl_context *ctx, const char *reason)
    _mesa_DeleteHashTable(glthread->VAOs);
 
    ctx->GLThread.enabled = false;
+   ctx->CurrentClientDispatch = ctx->CurrentServerDispatch;
 
-   /* Remove ourselves from the dispatch table except if another ctx/thread
-    * already installed a new dispatch table.
-    *
-    * Typically glxMakeCurrent will bind a new context (install new table) then
-    * old context might be deleted.
-    */
+   /* Update the dispatch only if the context is current. */
    if (_glapi_get_dispatch() == ctx->MarshalExec) {
-       ctx->CurrentClientDispatch = ctx->CurrentServerDispatch;
        _glapi_set_dispatch(ctx->CurrentClientDispatch);
    }
 }

src/mesa/main/mtypes.h

@@ -5225,8 +5225,7 @@ struct gl_context
    struct _glapi_table *ContextLost;
    /**
     * Dispatch table used to marshal API calls from the client program to a
-    * separate server thread.  NULL if API calls are not being marshalled to
-    * another thread.
+    * separate server thread.
     */
    struct _glapi_table *MarshalExec;
    /**