Always print leading zeros in mosquitto_sub when output format is hex.

Closes #1066.

Thanks to skiizo.

Bug: https://github.com/eclipse/mosquitto/issues/1066

ChangeLog.txt

@@ -1,3 +1,11 @@
+1.5.5 - 201812xx
+================
+
+Client:
+- Always print leading zeros in mosquitto_sub when output format is hex.
+  Closes #1066.
+
+
 1.5.4 - 20181108
 ================
 

client/sub_client_output.c

@@ -85,11 +85,11 @@ static void write_payload(const unsigned char *payload, int payloadlen, int hex)
 		(void)fwrite(payload, 1, payloadlen, stdout);
 	}else if(hex == 1){
 		for(i=0; i<payloadlen; i++){
-			fprintf(stdout, "%x", payload[i]);
+			fprintf(stdout, "%02x", payload[i]);
 		}
 	}else if(hex == 2){
 		for(i=0; i<payloadlen; i++){
-			fprintf(stdout, "%X", payload[i]);
+			fprintf(stdout, "%02X", payload[i]);
 		}
 	}
 }