virsh: perf: Don't leak domain

After failing to parse the perf event list, the code would return
failure without freeing the previously acquired object. Rearrange the
code to avoid the problem.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1329046

tools/virsh-domain.c

@@ -8623,13 +8623,13 @@ cmdPerf(vshControl *ctl, const vshCmd *cmd)
     if (live)
         flags |= VIR_DOMAIN_AFFECT_LIVE;
 
-    if (!(dom = virshCommandOptDomain(ctl, cmd, NULL)))
-        return false;
-
     if (vshCommandOptStringReq(ctl, cmd, "enable", &enable) < 0 ||
         vshCommandOptStringReq(ctl, cmd, "disable", &disable) < 0)
         return false;
 
+    if (!(dom = virshCommandOptDomain(ctl, cmd, NULL)))
+        return false;
+
     if (enable && virshParseEventStr(enable, true, &params,
                                      &nparams, &maxparams) < 0)
         goto cleanup;