gobj: Fix Texture render_to_texture flag garbage after CData copy

panda/src/gobj/texture.I

@@ -26,6 +26,7 @@ INLINE PT(Texture) Texture::
 make_copy() const {
   PT(Texture) tex = make_copy_impl();
   CDWriter cdata_tex(tex->_cycler, true);
+  cdata_tex->_render_to_texture = false;
   cdata_tex->inc_properties_modified();
   cdata_tex->inc_image_modified();
   cdata_tex->inc_simple_image_modified();

panda/src/gobj/texture.cxx

@@ -10710,6 +10710,7 @@ CData() {
 Texture::CData::
 CData(const Texture::CData &copy) {
   _num_mipmap_levels_read = 0;
+  _render_to_texture = copy._render_to_texture;
 
   do_assign(&copy);