[Coverage] Complete top-level deferred regions before labels

The area immediately after a terminated region in the function top-level
should have the same count as the label it precedes.

This solves another problem with wrapped segments. Consider:

  1| a:
  2|   return 0;
  3| b:
  4|   return 1;

Without a gap area starting after the first return, the wrapped segment
from line 2 would make it look like line 3 is executed, when it's not.

rdar://35373009

llvm-svn: 317759