Check if wordexp succeeds before using its output

When wordexp returns non-zero values, the wordexp_t output is not guaranteed to be in good shape and wordfreeing it might cause segfaults:

#include <stdio.h>
#include <stdlib.h>
#include <wordexp.h>

int main(void) {
  wordexp_t p;
  char **w;

  printf("%d\n", wordexp("wayland;fcitx;ibus", &p, 0));
  w = p.we_wordv;
  for (size_t i = 0; i < p.we_wordc; i++)
    printf("%s\n", w[i]);
  wordfree(&p); //<----------- segfaults here
  return 0;
}

$ gcc a.c
$ ./a.out
2
[1]    32922 segmentation fault (core dumped)  ./a.out

This PR checks the return value of wordexp and calls wordfree accordingly.

Reproduction Steps

Open lxqt-config-session and add an enviroment variable like QT_IM_MODULES=wayland;fcitx;ibus.
Check ~/.config/lxqt/session.conf for this line QT_IM_MODULES="wayland;fcitx;ibus", and note that wayland;fcitx;ibus is an invalid input string for wordexp.
Run lxqt-session and observe the segfault.

Other details

lxqt-session installed from the Arch Linux repository differs from lxqt-session compiled from source (both v2.0.0):

Arch one:

#0  0x000055555556b7fb in QByteArrayView::QByteArrayView<char*, true> (
  data=<error reading variable: Cannot access memory at address 0x0>, this=<optimized out>)
  at /usr/include/qt6/QtCore/qbytearrayview.h:150
#1  lxqt_setenv (value=<synthetic pointer>..., env=0x5555555e0070 "QT_IM_MODULES")
  at /usr/src/debug/lxqt-session/lxqt-session-2.0.0/lxqt-session/src/lxqtmodman.cpp:429
(gdb) print p
$7 = {we_wordc = 1, we_wordv = 0x0, we_offs = 0}

Note that we_wordv is a null pointer, which seems like garbage value from the uninitialized wordexp_t p.

Compiled from source one: segfault at wordfree.

But this PR should be able to handle both cases.

lxqt / lxqt-session

Check if wordexp succeeds before using its output #525

Reproduction Steps

Other details