Refresh Formula overlay after loading LFO preset or undo/redo, if applicable

[mkruselj]

Closes #7308

[baconpaul]

This is clever, and close, but not quite complete.

Rather than doing an || you should do a loop. If formula and mseg are both open this will fail.

So whereas before it was

if (isopen(mseg) )
   blah

and you changed it to

if (isopen(mseg) || isopen (formula))
   which = is mseg ? mseg : formula

you should change it to

for( const auto &cand : { mseg_enum, formula_enum } )
{
   if (isopen(cand))
      then do it
}

so if you have both open and torn out they will simultaneously refresh

[baconpaul]

See inline comment; we can make it a loop over enum type and work with both open.

Done according to suggestion

[baconpaul]

LGTM!