Skip over state declarations at run time
Tweak multiple nextstate optimisation further

There was still one niggling nulled nextstate in the execution
sequence in cases like this (the one numbered 4):

$ ./perl -Ilib  -MO=Concise -e 'time; our $x; our $y; time'
7  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v:{ ->3
3     <0> time[t1] v ->4
-     <0> ex-nextstate v ->5
-     <1> rv2sv vK/OURINTR,1 ->4
-        <$> gv(*x) s ->-
4     <0> ex-nextstate v ->5
-     <1> rv2sv vK/OURINTR,1 ->5
-        <$> gv(*y) s ->-
5     <;> nextstate(main 3 -e:1) v:{ ->6
6     <0> time[t4] v ->7
-e syntax OK