virsh-snapshot: Reject --no-metadata together with --print-xml

Manual for "virsh snapshot-create-as" states that --no-metadata and
--print-xml are incompatible. Honor this detail in the code.

tools/virsh-snapshot.c

@@ -412,8 +412,14 @@ cmdSnapshotCreateAs(vshControl *ctl, const vshCmd *cmd)
     unsigned int flags = 0;
     const vshCmdOpt *opt = NULL;
 
-    if (vshCommandOptBool(cmd, "no-metadata"))
+    if (vshCommandOptBool(cmd, "no-metadata")) {
+        if (vshCommandOptBool(cmd, "print-xml")) {
+            vshError(ctl, "%s",
+                     _("--print-xml is incompatible with --no-metadata"));
+            return false;
+        }
         flags |= VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA;
+    }
     if (vshCommandOptBool(cmd, "halt"))
         flags |= VIR_DOMAIN_SNAPSHOT_CREATE_HALT;
     if (vshCommandOptBool(cmd, "disk-only"))