Fixes the missing 'app' directory:
Traceback (most recent call last):
File "/data/dwrobel1/rdkv/rpi-flutter-3/build-raspberrypirdkhybrefapp/tmp/sysroots/x86_64-linux/usr/bin/gdbus-codegen", line 39, in <module>
sys.exit(codegen_main.codegen_main())
File "/data/dwrobel1/rdkv/rpi-flutter-3/build-raspberrypirdkhybrefapp/tmp/sysroots/x86_64-linux/usr/share/glib-2.0/codegen/codegen_main.py", line 186, in codegen_main
h = open(c_code + '.h', 'w')
FileNotFoundError: [Errno 2] No such file or directory: './app/flatpak-permission-dbus-generated.h'
make: *** [app/flatpak-permission-dbus-generated.c] Error 1
make: *** Waiting for unfinished jobs....