formats: Fix readback condition for depth buffers

The old implementation of vrend_add_formats used to check color readback
format even if a depth buffer is bound. As no texture is attached to the
color buffer for such a FBO, it makes glGetIntegerv with
GL_IMPLEMENTATION_COLOR_READ_TYPE fail, and the error can trigger the
GL_NO_ERROR assertion in the function.

Check only if the depth buffer can be read in such a case.

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>

src/vrend_formats.c

@@ -536,7 +536,7 @@ static void vrend_add_formats(struct vrend_format_table *table, int num_entries)
        formats that are supported as destination formats by glReadPixels. */
     if (is_desktop_gl ||
         (status == GL_FRAMEBUFFER_COMPLETE &&
-         ((is_depth && depth_stencil_formats_can_readback(table[i].format)) ||
+         (is_depth ? depth_stencil_formats_can_readback(table[i].format) :
                      color_format_can_readback(&table[i], gles_ver))))
        flags |= VIRGL_TEXTURE_CAN_READBACK;