[FAB-8017] Peer CLI fetch cmd error assignment issue

This CR fixes the fetch command's error assignment to ensure the
correct errors are being assigned and checked before proceeding.
With this fix, the end user will receive the correct error message
instead of a error message related to marshaling a nil value.

Change-Id: I39a32291357ff01f82e1bbd4df2ef6665f77d50b
Signed-off-by: Will Lahti <wtlahti@us.ibm.com>

Author: wlahti

peer/channel/fetchconfig.go

@@ -69,18 +69,18 @@ func fetch(cmd *cobra.Command, args []string, cf *ChannelCmdFactory) error {
 	case "newest":
 		block, err = cf.DeliverClient.getNewestBlock()
 	case "config":
-		iBlock, err := cf.DeliverClient.getNewestBlock()
-		if err != nil {
-			return err
+		iBlock, err2 := cf.DeliverClient.getNewestBlock()
+		if err2 != nil {
+			return err2
 		}
-		lc, err := utils.GetLastConfigIndexFromBlock(iBlock)
-		if err != nil {
-			return err
+		lc, err2 := utils.GetLastConfigIndexFromBlock(iBlock)
+		if err2 != nil {
+			return err2
 		}
 		block, err = cf.DeliverClient.getSpecifiedBlock(lc)
 	default:
-		num, err := strconv.Atoi(args[0])
-		if err != nil {
+		num, err2 := strconv.Atoi(args[0])
+		if err2 != nil {
 			return fmt.Errorf("fetch target illegal: %s", args[0])
 		}
 		block, err = cf.DeliverClient.getSpecifiedBlock(uint64(num))