dri: fromPlanar() can return NULL as a valid result

It was assumed that fromPlanar() could return NULL to mean
that the planar image is the same as the parent DRI image.
That assumption wasn't made everywhere though.

Let's fix things and make sure that all callers understand
a NULL result

Signed-off-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Daniel Stone <daniels@collabora.com>

src/egl/drivers/dri2/egl_dri2.c

@@ -1966,7 +1966,8 @@ dri2_create_image_wayland_wl_buffer(_EGLDisplay *disp, _EGLContext *ctx,
    }
 
    dri_image = dri2_dpy->image->fromPlanar(buffer->driver_buffer, plane, NULL);
-
+   if (dri_image == NULL && plane == 0)
+      dri_image = dri2_dpy->image->dupImage(buffer->driver_buffer, NULL);
    if (dri_image == NULL) {
       _eglError(EGL_BAD_PARAMETER, "dri2_create_image_wayland_wl_buffer");
       return NULL;

src/egl/drivers/dri2/platform_wayland.c

@@ -814,13 +814,10 @@ create_wl_buffer(struct dri2_egl_display *dri2_dpy,
          int stride, offset;
          int fd = -1;
 
-         if (i == 0)
-            p_image = image;
-         else
-            p_image = dri2_dpy->image->fromPlanar(image, i, NULL);
+         p_image = dri2_dpy->image->fromPlanar(image, i, NULL);
          if (!p_image) {
-            zwp_linux_buffer_params_v1_destroy(params);
-            return NULL;
+            assert(i == 0);
+            p_image = image;
          }
 
          query = dri2_dpy->image->queryImage(p_image,

src/gbm/backends/dri/gbm_dri.c

@@ -849,6 +849,7 @@ gbm_dri_bo_get_offset(struct gbm_bo *_bo, int plane)
       dri->image->queryImage(image, __DRI_IMAGE_ATTRIB_OFFSET, &offset);
       dri->image->destroyImage(image);
    } else {
+      assert(plane == 0);
       dri->image->queryImage(bo->image, __DRI_IMAGE_ATTRIB_OFFSET, &offset);
    }
 

src/loader/loader_dri3_helper.c

@@ -1288,7 +1288,10 @@ loader_dri3_create_image(xcb_connection_t *c,
 
    ret = image->fromPlanar(image_planar, 0, loaderPrivate);
 
-   image->destroyImage(image_planar);
+   if (!ret)
+      ret = image_planar;
+   else
+      image->destroyImage(image_planar);
 
    return ret;
 }