Backport of security: fix AliasCheck panic into release/1.19.x (#21341)

* backport of commit aeba4bc804

* backport of commit 8c5b157f7b

---------

Co-authored-by: dduzgun-security <deniz.duzgun@hashicorp.com>

.changelog/21339.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+core: Fix panic runtime error on AliasCheck
+```

agent/checks/alias.go

@@ -144,6 +144,9 @@ func (c *CheckAlias) runLocal(stopCh chan struct{}) {
 type CheckIfServiceIDExists func(*structs.ServiceID) bool
 
 func (c *CheckAlias) checkServiceExistsOnRemoteServer(serviceID *structs.ServiceID) (bool, error) {
+	if serviceID == nil {
+		return false, fmt.Errorf("serviceID cannot be nil")
+	}
 	args := c.RPCReq
 	args.Node = c.Node
 	args.AllowStale = true