mega fix

So turns out multiform megas with the same stone are still bugged in v18.
But here's the fix.
in `def getMegaForm`, find `if megaStone>0 && self.hasItem?(megaStone)`
and replace with
```ruby
      if megaStone>0 && self.hasItem?(megaStone) &&
          (self.formSimple==pbGetSpeciesData(@species,i,SpeciesUnmegaForm) ||
          self.formSimple==i)
```