qobject: Clean up around qtype_code

QTYPE_NONE is a sentinel value.  No QObject has this type code.
Document it properly.

Fix dump_qobject() to abort() on QTYPE_NONE, just like for any other
invalid type code.

Fix to_json() to abort() on all invalid type codes, not just
QTYPE_MAX.

Clean up Property member qtype's type: it's a qtype_code.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

block/qapi.c

@@ -523,9 +523,6 @@ static void dump_qobject(fprintf_function func_fprintf, void *f,
             QDECREF(value);
             break;
         }
-        case QTYPE_NONE:
-            break;
-        case QTYPE_MAX:
         default:
             abort();
     }

include/hw/qdev-core.h

@@ -226,7 +226,7 @@ struct Property {
     PropertyInfo *info;
     int          offset;
     uint8_t      bitnr;
-    uint8_t      qtype;
+    qtype_code   qtype;
     int64_t      defval;
     int          arrayoffset;
     PropertyInfo *arrayinfo;

include/qapi/qmp/qobject.h

@@ -36,7 +36,7 @@
 #include <assert.h>
 
 typedef enum {
-    QTYPE_NONE,
+    QTYPE_NONE,    /* sentinel value, no QObject has this type code */
     QTYPE_QINT,
     QTYPE_QSTRING,
     QTYPE_QDICT,

qobject/qjson.c

@@ -260,9 +260,8 @@ static void to_json(const QObject *obj, QString *str, int pretty, int indent)
     }
     case QTYPE_QERROR:
         /* XXX: should QError be emitted? */
-    case QTYPE_NONE:
         break;
-    case QTYPE_MAX:
+    default:
         abort();
     }
 }