RNA: Add RNA_property_string_set_bytes

This is needed to set values that contain zero bytes
(where the length isn't fixed).

source/blender/python/intern/bpy_rna.c

@@ -1751,10 +1751,8 @@ static int pyrna_py_to_prop(
 						return -1;
 					}
 					else {
-						/* same as unicode */
-						/* XXX, this is suspect but needed for function calls, need to see if theres a better way */
 						if (data) *((char **)data) = (char *)param;
-						else RNA_property_string_set(ptr, prop, param);
+						else RNA_property_string_set_bytes(ptr, prop, param, PyBytes_Size(value));
 					}
 				}
 				else {