fix texture loading when starting from SD card
With flow3r-firmare v1.2.0 loading apps from /flash/apps and /sd/apps/ is now supported. And app_ctx.bundle_path is now available to access the appropriate app's directory.
So using it to fix missing textures when starting the app from the SD card for instance.
Signed-off-by: Linus Lüssing linus.luessing@c0d3.blue