don't panic if we don't have any snapshots when checking the age.

report from behrens@bytemine.net

snapshots_age.go

@@ -29,6 +29,9 @@ func (x *SnapshotsAgeCommand) Execute(args []string) error {
 	if error != nil {
 		Unknown("Error retrieving snapshots")
 	}
+	if snapshot == nil {
+		Unknown("No snapshots found")
+	}
 
 	warningDuration := time.Duration(x.Warning) * time.Hour
 	criticalDuration := time.Duration(x.Critical) * time.Hour