Reintroduce assemble_element guard for have_gravity and have_source
Reintroduce assemble_element guard for have_gravity and have_source

iakovos-panourgias/fluidity,rjferrier/fluidity,iakovos-panourgias/fluidity,rjferrier/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,rjferrier/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,rjferrier/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,jrper/fluidity,jrper/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,iakovos-panourgias/fluidity,iakovos-panourgias/fluidity,rjferrier/fluidity