[#55] policy: Swap signature check order

While implementing the changes for FrostFS ID it became obvious, that
committee signature check can be rather costly (`getCommittee` call +
multiaddress construction + checking witness). In real scenarious it
will mostly fail, so it makes sense do it last.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

policy/policy_contract.go

@@ -47,14 +47,13 @@ func _deploy(data any, isUpdate bool) {
 }
 
 func checkAuthorization(ctx storage.Context) {
-	if runtime.CheckWitness(common.AlphabetAddress()) {
-		return
-	}
-
 	admin := getAdmin(ctx)
 	if admin != nil && runtime.CheckWitness(admin) {
 		return
 	}
+	if runtime.CheckWitness(common.AlphabetAddress()) {
+		return
+	}
 
 	panic(ErrNotAutorized)
 }