applied the patch to xmlTextWriterStartPI() suggested by Daniel Schulman

* xmlwriter.c: applied the patch to xmlTextWriterStartPI()
  suggested by Daniel Schulman in #128313
Daniel
diff --git a/xmlwriter.c b/xmlwriter.c
index 1585933..6b2fea2 100644
--- a/xmlwriter.c
+++ b/xmlwriter.c
@@ -2110,6 +2110,10 @@
                     sum += count;
                     p->state = XML_TEXTWRITER_TEXT;
                     break;
+		case XML_TEXTWRITER_NONE:
+		case XML_TEXTWRITER_TEXT:
+		case XML_TEXTWRITER_DTD:
+		    break;
                 case XML_TEXTWRITER_PI:
                 case XML_TEXTWRITER_PI_TEXT:
                     xmlGenericError(xmlGenericErrorContext,