network: Resolve Coverity FORWARD_NULL

If the VIR_STRDUP(exptime,...) fails, then we will jump to cleanup,
no need to check if exptime is set which causes Coverity to issue
a complaint in the virStrToLong_ll call because there wasn't a check
for a NULL value while there was one for the reference right after
the VIR_STRDUP().
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

src/network/leaseshelper.c

@@ -180,8 +180,7 @@ main(int argc, char **argv)
         goto cleanup;
 
     /* Removed extraneous trailing space in DNSMASQ_LEASE_EXPIRES (dnsmasq < 2.52) */
-    if (exptime &&
-        exptime[strlen(exptime) - 1] == ' ')
+    if (exptime[strlen(exptime) - 1] == ' ')
         exptime[strlen(exptime) - 1] = '\0';
 
     /* Check if it is an IPv6 lease */