Fix quadratic runtime in HTML push parser with null bytes

Null bytes in the input stream do not necessarily signal an EOF
condition. Check the stream pointers for EOF to avoid quadratic
rescanning of input data.

Note that the CUR_CHAR macro used in functions like htmlParseCharData
calls htmlCurrentChar which translates null bytes.

Found by OSS-Fuzz.

HTMLparser.c

@@ -5832,7 +5832,7 @@ htmlParseTryOrFinish(htmlParserCtxtPtr ctxt, int terminate) {
 			xmlGenericError(xmlGenericErrorContext,
 				"HPP: Parsing char data\n");
 #endif
-                        while ((cur != '<') && (cur != 0)) {
+                        while ((cur != '<') && (in->cur < in->end)) {
                             if (cur == '&') {
 			        htmlParseReference(ctxt);
                             } else {