Halt parser in case of encoding error

Should fix crbug.com/793715, although I wasn't able to reproduce the
issue.
diff --git a/parser.c b/parser.c
index d1ce8b5..5e800e1 100644
--- a/parser.c
+++ b/parser.c
@@ -12218,6 +12218,7 @@
 		    /* TODO 2.6.0 */
 		    xmlGenericError(xmlGenericErrorContext,
 				    "xmlParseChunk: encoder error\n");
+                    xmlHaltParser(ctxt);
 		    return(XML_ERR_INVALID_ENCODING);
 		}
 		xmlBufSetInputBaseCur(in->buffer, ctxt->input, base, current);