Fix large parse of file from memory

https://bugzilla.redhat.com/show_bug.cgi?id=862969
The new code trying to detect excessive input lookup would
just get wrong sometimes in the case of very large file parsed
directly from memory.

libxml.h

@@ -91,6 +91,8 @@ void __xmlGlobalInitMutexDestroy(void);
 int __xmlRandom(void);
 #endif
 
+int xmlNop(void);
+
 #ifdef IN_LIBXML
 #ifdef __GNUC__
 #ifdef PIC

parser.c

@@ -2025,6 +2025,7 @@ static void xmlSHRINK (xmlParserCtxtPtr ctxt) {
 static void xmlGROW (xmlParserCtxtPtr ctxt) {
     if ((((ctxt->input->end - ctxt->input->cur) > XML_MAX_LOOKUP_LIMIT) ||
          ((ctxt->input->cur - ctxt->input->base) > XML_MAX_LOOKUP_LIMIT)) &&
+         ((ctxt->input->buf) && (ctxt->input->buf->readcallback != xmlNop)) &&
         ((ctxt->options & XML_PARSE_HUGE) == 0)) {
         xmlFatalErr(ctxt, XML_ERR_INTERNAL_ERROR, "Huge input lookup");
         ctxt->instate = XML_PARSER_EOF;

xmlIO.c

@@ -800,7 +800,7 @@ xmlCheckFilename (const char *path)
     return 1;
 }
 
-static int
+int
 xmlNop(void) {
     return(0);
 }