zink: Always fill external_only in zink_query_dmabuf_modifiers

Fix piglit.spec@ext_image_dma_buf_import@ext_image_dma_buf_import-modifiers
randomly skipping some tests as external_only content was never initialized.

Cc: mesa-stable

Reviewed-by: default avatarMike Blumenkrantz <michael.blumenkrantz@gmail.com>
Signed-off-by: Mary Guillemard <mary.guillemard@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26305>
(cherry picked from commit b6d828576e)

.pick_status.json

@@ -1264,7 +1264,7 @@
         "description": "zink: Always fill external_only in zink_query_dmabuf_modifiers",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null,
         "notes": null

src/gallium/drivers/zink/zink_screen.c

@@ -2455,8 +2455,12 @@ zink_query_dmabuf_modifiers(struct pipe_screen *pscreen, enum pipe_format format
 {
    struct zink_screen *screen = zink_screen(pscreen);
    *count = screen->modifier_props[format].drmFormatModifierCount;
-   for (int i = 0; i < MIN2(max, *count); i++)
+   for (int i = 0; i < MIN2(max, *count); i++) {
+      if (external_only)
+         external_only[i] = 0;
+
       modifiers[i] = screen->modifier_props[format].pDrmFormatModifierProperties[i].drmFormatModifier;
+   }
 }
 
 static bool