plugin/file: fix file leak (#5687)

plugin/file/setup.go

@@ -93,18 +93,27 @@ func fileParse(c *caddy.Controller) (Zones, error) {
 			openErr = err
 		}
 
+		err = func() error {
+			defer reader.Close()
+
 			for i := range origins {
 				z[origins[i]] = NewZone(origins[i], fileName)
 				if openErr == nil {
 					reader.Seek(0, 0)
 					zone, err := Parse(reader, origins[i], fileName, 0)
 					if err != nil {
-					return Zones{}, err
+						return err
 					}
 					z[origins[i]] = zone
 				}
 				names = append(names, origins[i])
 			}
+			return nil
+		}()
+
+		if err != nil {
+			return Zones{}, err
+		}
 
 		for c.NextBlock() {
 			switch c.Val() {