mesa: initialize gl_renderbuffer::Depth in core

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Tested-by: Ian Romanick <ian.d.romanick@intel.com>
diff --git a/src/mesa/main/fbobject.c b/src/mesa/main/fbobject.c
index 3650627..861885d 100644
--- a/src/mesa/main/fbobject.c
+++ b/src/mesa/main/fbobject.c
@@ -411,6 +411,7 @@
    rb->InternalFormat = texImage->InternalFormat;
    rb->Width = texImage->Width2;
    rb->Height = texImage->Height2;
+   rb->Depth = texImage->Depth2;
    rb->NumSamples = texImage->NumSamples;
    rb->TexImage = texImage;