Fix recalbox.version does not exist on non-docker builds

The Docker file includes a command to create a recalbox.version file. This file is needed by the recalbox-patch-target.sh script. When compiling recalbox without using Docker, the recalbox.version file is not created and then the following error occurs:

Executing post-build script /home/thomas/git/recalbox/board/recalbox/recalbox-patch-target.sh cat: /home/thomas/git/recalbox/output/target/recalbox/recalbox.version: Aucun fichier ou dossier de ce type Makefile:697 : la recette pour la cible « target-finalize » a échouée make[1]: *** [target-finalize] Erreur 1 make[1] : on quitte le répertoire « /home/thomas/git/recalbox/buildroot » Makefile:25 : la recette pour la cible « buildBR » a échouée make: *** [buildBR] Erreur 2

The proposed MR changes recalbox-patch-target.sh to test for the existence of the recalbox.version file. If this file does not exist, it creates it with the default value "development" instead of failing the build.