Instead of allocating a single 0 char, set the `char *` DNA pointer to
null. This avoids the overhead of allocating and copying single-bytes.
rBeed45b655c9f didn't do this for safety reasons, but I checked the
existing uses of this behavior in DNA/RNA. Out of 43 total `char *`
members, this change only affects 7 recently added properties.
For a complete list, see the patch description.
Differential Revision: https://developer.blender.org/D14779
35b4e3a350