[vte] conv: Fix crash after multiple encoding changes

[Egmont Koblinger <egmontkob src gnome org>]

commit cb315a4c4162a543f910cb0c11a8cf91bd17b0e4
Author: Egmont Koblinger <egmont gmail com>
Date:   Sun Sep 23 12:55:46 2018 +0200

    conv: Fix crash after multiple encoding changes
    
    https://gitlab.gnome.org/GNOME/vte/issues/50

 src/vte.cc | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/vte.cc b/src/vte.cc
index 3055d622..6e4d85d1 100644
--- a/src/vte.cc
+++ b/src/vte.cc
@@ -1966,6 +1966,8 @@ Terminal::set_encoding(char const* codeset)
                         g_iconv_close(m_incoming_conv);
                 if (m_outgoing_conv != ((GIConv)-1))
                         g_iconv_close(m_outgoing_conv);
+                m_incoming_conv = (GIConv)-1;
+                m_outgoing_conv = (GIConv)-1;
         } else {
                 auto outconv = g_iconv_open(codeset, "UTF-8");
                 if (outconv == ((GIConv)-1))