patch 8.1.1064: no test for output conversion in the GTK GUI

Problem:    No test for output conversion in the GTK GUI.
Solution:   Add a simplistic test.
diff --git a/src/testdir/test_gui.vim b/src/testdir/test_gui.vim
index 7874fff..f1f2cdd 100644
--- a/src/testdir/test_gui.vim
+++ b/src/testdir/test_gui.vim
@@ -720,6 +720,21 @@
   let &guipty = guipty_saved
 endfunc
 
+func Test_encoding_conversion()
+  " GTK supports conversion between 'encoding' and "utf-8"
+  if has('gui_gtk')
+    let encoding_saved = &encoding
+    set encoding=latin1
+
+    " would be nice if we could take a screenshot
+    intro
+    " sets the window title
+    edit SomeFile
+
+    let &encoding = encoding_saved
+  endif
+endfunc
+
 func Test_shell_command()
   new
   r !echo hello
diff --git a/src/version.c b/src/version.c
index 1fa7429..b8b3c14 100644
--- a/src/version.c
+++ b/src/version.c
@@ -776,6 +776,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1064,
+/**/
     1063,
 /**/
     1062,