common: Add NULL checks for xrealloc in make_string cli_hush.c

- Check return value of xrealloc for NULL.
- Free allocated memory and return NULL if xrealloc fails.
- Prevent NULL pointer dereference in strlen and strcat.

Triggers found by static analyzer Svace.

Signed-off-by: Anton Moryakov <ant.v.moryakov@gmail.com>
1 file changed