Fix some verification conditions

Author: mgrojo

src/coap_spark-channel.adb

@@ -303,7 +303,7 @@ is
                Input.Buffer'Length <= Buffer'Length
             then
                Length := RFLX.RFLX_Builtin_Types.Length (Input.Last);
-               Buffer (1 .. RFLX.RFLX_Builtin_Types.Index (Length)) :=
+               Buffer (1 .. RFLX.RFLX_Builtin_Types.Index'Base (Length)) :=
                  To_RFLX_Bytes (Input.Buffer);
             else
                Socket.Result :=

src/coap_spark-messages-encoding.adb

@@ -478,6 +478,8 @@ package body CoAP_SPARK.Messages.Encoding is
    is
    begin
 
+      Status := OK;
+
       if Data'Length = 0 then
 
          CoAP_SPARK.Log.Put_Line ("Options and payload are empty");

src/coap_spark-messages.ads

@@ -34,7 +34,7 @@ is
    type Content is record
       Options : CoAP_SPARK.Options.Lists.Vector;
       Format : Interfaces.Unsigned_32 := 0;
-      Payload : Payload_Ptr;
+      Payload : Payload_Ptr := null;
    end record;
 
    --  Log the content of a message according to the log levels for options and