Fix crash with crafted ini files.

If the key or value is bigger than 1024 we will end up in a buffer
overflow. The overflow is caught by _FORTIFY_SOURCE, so it's definitely
DoS-only.  Curiously, because of ample space in the stack frame, it does
not result in a crash without _FORTIFY_SOURCE in all cases.

Signed-off-by: Andreas Schneider <asn@samba.org>