v0.4.2: no more crash when your partner enters a wild battle

A wild battles fix (#6).

• No more crash when your partner enters a wild battle. The game stopped whenever your partner (the Pikachu or
  Eevee you started with) entered a wild battle while it was the one walking with you - leading the party or
  switched in. Early in the game nobody else walks with you, so that was the usual case. The battle brings in the
  field model of the Pokémon walking with you, and the kind of battle this mode uses has none for the partner.
  Until that is supported, in that situation touching a wild Pokémon starts the game's own catch, as without the
  mode.
• With another Pokémon walking with you, wild battles work, your partner included. 0.4.1 had sent some of those
  encounters to the catch too.

Tested with the zip built for this release, in fresh folders without MSYS2 on the PATH: Eevee and Pikachu load a save,
reach the world and open the menu. The wild battle rule was checked from the source tree with a Route 1 save (the
partner walking alone: the game's catch, no crash) and with a save where another Pokémon walks along (battles, the
partner entering included).

Updating from 0.4.x: with the game closed, unzip over your folder (keeps the game files, saves, translations and
settings). The game library is not rebuilt.