Fixing build

Build is failing due to a unused variable in json_tokener:

```
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -Wall -Werror -Wextra -Wwrite-strings -Wno-unused-parameter -std=gnu99 -D_GNU_SOURCE -D_REENTRANT -g -O2 -MT json_tokener.lo -MD -MP -MF .deps/json_tokener.Tpo -c json_tokener.c  -fPIC -DPIC -o .libs/json_tokener.o
json_tokener.c: In function ‘json_tokener_parse_ex’:
json_tokener.c:345:6: error: variable ‘size’ set but not used [-Werror=unused-but-set-variable]
cc1: all warnings being treated as errors
```