lib: json: Fix number parsing

Comparing *endptr with '\0' will always be true before replacing
*token->end with prev_end.

Jira: ZEP-1607
Change-Id: I224129586e15380d3919bfba3db4fcf38c28cb07
Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>
1 file changed