Previously, the following caused a segmentation fault:
json.stringify({[{}] = true})
This was caused by lua_tostring() returning NULL for anything but
strings and numbers, letting json_object_object_add crash.
This patch makes jsonc ignore all keys which have no string
representation altogether.
Signed-off-by: Jan-Philipp Litza <janphilipp@litza.de>
e32a877aa4