Idea is to replace hard-to-track (id->lib != NULL) 'is linked datablock' check everywhere in Blender by a macro doing the same thing. This will allow to easily spot those checks in future, and more importantly, to easily change it (see work done in asset-engine branch). Note: did not touch to readfile.c, since there most of the time 'id->lib' check actually concerns the pointer, and not a check whether ID is linked or not. Will have a closer look at it later. Reviewers: campbellbarton, brecht, sergey Differential Revision: https://developer.blender.org/D2082