dbConstAddLink bounds check dbrType

cf. 6c914d19c3

modules/database/src/ioc/db/dbConstLink.c

@@ -169,6 +169,9 @@ static long dbConstLoadScalar(struct link *plink, short dbrType, void *pbuffer)
         return dbPutConvertJSON(pstr, dbrType, pbuffer, &nReq);
     }
 
+    if(dbrType>=NELEMENTS(convert))
+        return S_db_badDbrtype;
+
     return convert[dbrType](pstr, pbuffer, NULL);
 }