JIT: don't set edge weights to zero for inconsistent profiles (#87947)

JIT: don't set edge weights to zero for inconsistent profiles (#87947)

With the advent of scalable profile counters (or even with the old racing
counters) counts might be approximate or inconsistent. When we run across a
negative count during reconstruction, set the afflicted count to a small
positive value instead of to zero, since zero has special meaning to the JIT.

The aim is to reduce some of the benchmark instability we are seeing in #87324.
Depending on exact counter values, we can see different sets of edge weights
(and hence block weights) from run to run.