Reset HTML parser input pointers on encoding failure

Call xmlBufResetInput before bailing out if switching the encoding
fails. Otherwise, the input pointers could be left in an invalid state.

Similar to commit f9e7997 for the
XML parser.

Thanks to Yunho Kim for the report.

Closes: #27

HTMLparser.c

@@ -3636,12 +3636,12 @@ htmlCheckEncodingDirect(htmlParserCtxtPtr ctxt, const xmlChar *encoding) {
 	    processed = ctxt->input->cur - ctxt->input->base;
 	    xmlBufShrink(ctxt->input->buf->buffer, processed);
 	    nbchars = xmlCharEncInput(ctxt->input->buf, 1);
+            xmlBufResetInput(ctxt->input->buf->buffer, ctxt->input);
 	    if (nbchars < 0) {
 		htmlParseErr(ctxt, XML_ERR_INVALID_ENCODING,
 		             "htmlCheckEncoding: encoder error\n",
 			     NULL, NULL);
 	    }
-            xmlBufResetInput(ctxt->input->buf->buffer, ctxt->input);
 	}
     }
 }