[meld] sourceview: Fix PangoLayout.set_text() usage for older pygobject (#488)

[Kai Willadsen <kaiw src gnome org>]

commit e4d4d05e7b1a0e7f08e50d28f5f8c2a0507d099c
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Mon Jul 20 17:43:48 2020 +1000

    sourceview: Fix PangoLayout.set_text() usage for older pygobject (#488)
    
    This override wasn't added until pygobject 3.31.1. Since it's a very
    minor convenience, it doesn't seem worth bumping our version requirement
    just for this.

 meld/sourceview.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meld/sourceview.py b/meld/sourceview.py
index 0c93ed87..0e1a9dc4 100644
--- a/meld/sourceview.py
+++ b/meld/sourceview.py
@@ -216,7 +216,7 @@ class MeldSourceView(GtkSource.View, SourceViewHelperMixin):
         if not getattr(self, '_approx_line_height', None):
             context = self.get_pango_context()
             layout = Pango.Layout(context)
-            layout.set_text('X')
+            layout.set_text('X', -1)
             _width, self._approx_line_height = layout.get_pixel_size()
 
         return self._approx_line_height