applied patch from Markus Keim fixing a problem with I/O callback

* xmlIO.c: applied patch from Markus Keim fixing a problem
  with I/O callback registration.
* include/libxml/xmlerror.h: fixed #122994 comment numbering
  for xmlParserErrors
Daniel
diff --git a/xmlIO.c b/xmlIO.c
index 88b5054..af8a44e 100644
--- a/xmlIO.c
+++ b/xmlIO.c
@@ -157,7 +157,6 @@
         xmlInputCallbackTable[i].readcallback = NULL;
         xmlInputCallbackTable[i].closecallback = NULL;
     }
-    xmlInputCallbackInitialized = 0;
 
     xmlInputCallbackNr = 0;
     xmlInputCallbackInitialized = 0;
@@ -183,7 +182,6 @@
         xmlOutputCallbackTable[i].writecallback = NULL;
         xmlOutputCallbackTable[i].closecallback = NULL;
     }
-    xmlOutputCallbackInitialized = 0;
 
     xmlOutputCallbackNr = 0;
     xmlOutputCallbackInitialized = 0;
@@ -1436,6 +1434,7 @@
     xmlInputCallbackTable[xmlInputCallbackNr].opencallback = openFunc;
     xmlInputCallbackTable[xmlInputCallbackNr].readcallback = readFunc;
     xmlInputCallbackTable[xmlInputCallbackNr].closecallback = closeFunc;
+    xmlInputCallbackInitialized = 1;
     return(xmlInputCallbackNr++);
 }
 
@@ -1461,6 +1460,7 @@
     xmlOutputCallbackTable[xmlOutputCallbackNr].opencallback = openFunc;
     xmlOutputCallbackTable[xmlOutputCallbackNr].writecallback = writeFunc;
     xmlOutputCallbackTable[xmlOutputCallbackNr].closecallback = closeFunc;
+    xmlOutputCallbackInitialized = 1;
     return(xmlOutputCallbackNr++);
 }