rts: Correct handling of LARGE ARR_WORDS in LDV profiler
This implements the correct fix for Trac #11627 by skipping over the slop
(which is zeroed) rather than adding special case logic for LARGE
ARR_WORDS which runs the risk of not performing a correct census by
ignoring any subsequent blocks.
This approach implements similar logic to that in Sanity.c
(cherry picked from commit 808a87ff9be4d92d3124c7d70104f6a339880021)