[irhydra] workaround for position assignment bug in V8
[irhydra] workaround for position assignment bug in V8

Sometimes V8 produces incorrect positions for the first loop body
block: it points to the loops init clause instead of pointing past it.
This confuses our loop finding algorithm that skips init clause.

Try working around this by looking at our predecessor: if it's a direct
fall-through and its position is further ahead compared to ours than
something went wrong — take its position.

mraleph/irhydra,mraleph/irhydra,mraleph/irhydra