mesa: don't crash on incorrect texture use

Cc: mesa-stable
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4995

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11603>
(cherry picked from commit 328ea8e04a)

.pick_status.json

@@ -508,7 +508,7 @@
         "description": "mesa: don't crash on incorrect texture use",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null
     },

src/mesa/main/mipmap.c

@@ -1913,6 +1913,10 @@ _mesa_prepare_mipmap_levels(struct gl_context *ctx,
 {
    const struct gl_texture_image *baseImage =
       _mesa_select_tex_image(texObj, texObj->Target, baseLevel);
+
+   if (baseImage == NULL)
+      return;
+
    const GLint border = 0;
    GLint width = baseImage->Width;
    GLint height = baseImage->Height;

src/mesa/state_tracker/st_cb_texture.c

@@ -2751,7 +2751,8 @@ st_finalize_texture(struct gl_context *ctx,
 
    firstImage = st_texture_image_const(stObj->base.Image[cubeMapFace]
                                        [stObj->base.Attrib.BaseLevel]);
-   assert(firstImage);
+   if (!firstImage)
+      return false;
 
    /* If both firstImage and stObj point to a texture which can contain
     * all active images, favour firstImage.  Note that because of the