lib: Use g_clear_pointer() more

lib: Use g_clear_pointer() more

This change was generated using the following spatch:

  @ rule1 @
  expression a;
  identifier f;
  @@
    <...
  - f(*a);
    ... when != a;
  - *a = NULL;
  + g_clear_pointer(a, f);
    ...>

  @ rule2 @
  expression a;
  identifier f;
  @@
    <...
  - f(a);
    ... when != a;
  - a = NULL;
  + g_clear_pointer(&a, f);
    ...>

Then, I left some of the changes out, like tools/nss/ (which
doesn't link with glib) and put back a comment in
qemuBlockJobProcessEventCompletedActiveCommit() which coccinelle
decided to remove (I have no idea why).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>