demos: Skip widgets if JSON-C is not available
demos: Skip widgets if JSON-C is not available

When JSON-C is not available, also skip the widgets demos folder too.

Signed-off-by: Rob Loach <4c58b37a60edcb7f0c248e9ae9d561bcb065f992@gmail.com>
Reviewed-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim