[balsa/gtk3] Fix a bug in the configure script

[Peter Bloomfield <peterb src gnome org>]

commit d35e56ef1ac51a18f0f48dcd80f2f2260f6ba92a
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Thu Jul 28 13:31:00 2016 -0400

    Fix a bug in the configure script
    
        Fix a bug in the configure script discovered by Jack
        <URL:https://mail.gnome.org/archives/balsa-list/2016-July/msg00039.html>
    
        * configure.ac: when no external html-to-text converter could
          be found, undef HTML2TEXT instead of defining it to "".

 ChangeLog    |    8 ++++++++
 configure.ac |    6 +++---
 2 files changed, 11 insertions(+), 3 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index f82e94f..1ab89ad 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2016-07-28  Albrecht Dreß
+
+       Fix a bug in the configure script discovered by Jack
+       <URL:https://mail.gnome.org/archives/balsa-list/2016-July/msg00039.html>
+
+       * configure.ac: when no external html-to-text converter could
+         be found, undef HTML2TEXT instead of defining it to "".
+
 2016-07-27  Peter Bloomfield  <pbloomfield bellsouth net>
 
        Andreas Schmidt suggested an improvement to the list of identities
diff --git a/configure.ac b/configure.ac
index d6fe7c5..756a02b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -361,9 +361,9 @@ case "$use_html_widget" in
                        html2markdown.py2 \
                        html2markdown.py3 \
                        html2text],
-                      no)
-        if test x"$ac_cv_path_HTML2TEXT" != "xno" ; then
-            AC_DEFINE_UNQUOTED(HTML2TEXT, "$ac_cv_path_HTML2TEXT",
+                      [no])
+        if test x"$HTML2TEXT" != "xno" ; then
+            AC_DEFINE_UNQUOTED(HTML2TEXT, "$HTML2TEXT",
                                [Path to html2text program.])
                else
                        AC_MSG_WARN([You cannot properly quote html-only messags.])