Avoid memory leak if xmlParserInputBufferCreateIO fails

For https://bugzilla.gnome.org/show_bug.cgi?id=643949

In case of error on an IO creation input the given context
is terminated with the given close function, except if the
error happened in xmlParserInputBufferCreateIO. This can
lead to a resource leak which is fixed by this patch.
diff --git a/HTMLparser.c b/HTMLparser.c
index 2eb3fb4..bf15c6a 100644
--- a/HTMLparser.c
+++ b/HTMLparser.c
@@ -6780,8 +6780,11 @@
 
     input = xmlParserInputBufferCreateIO(ioread, ioclose, ioctx,
                                          XML_CHAR_ENCODING_NONE);
-    if (input == NULL)
+    if (input == NULL) {
+        if (ioclose != NULL)
+            ioclose(ioctx);
         return (NULL);
+    }
     ctxt = htmlNewParserCtxt();
     if (ctxt == NULL) {
         xmlFreeParserInputBuffer(input);
@@ -6980,8 +6983,11 @@
 
     input = xmlParserInputBufferCreateIO(ioread, ioclose, ioctx,
                                          XML_CHAR_ENCODING_NONE);
-    if (input == NULL)
+    if (input == NULL) {
+        if (ioclose != NULL)
+            ioclose(ioctx);
         return (NULL);
+    }
     stream = xmlNewIOInputStream(ctxt, input, XML_CHAR_ENCODING_NONE);
     if (stream == NULL) {
         xmlFreeParserInputBuffer(input);