[meld] style: Make allowances for a missing style consistently

[Kai Willadsen <kaiw src gnome org>]

commit 506788de7618b0e2c132fdfd2ade9fbb15084f39
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sat Jul 13 07:18:38 2019 +1000

    style: Make allowances for a missing style consistently

 bin/meld      | 0
 meld/style.py | 3 ++-
 2 files changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/bin/meld b/bin/meld
old mode 100644
new mode 100755
diff --git a/meld/style.py b/meld/style.py
index 1cf330de..27a6aed0 100644
--- a/meld/style.py
+++ b/meld/style.py
@@ -72,7 +72,8 @@ def set_base_style_scheme(
 
     manager = GtkSource.StyleSchemeManager.get_default()
     base_style_scheme = manager.get_scheme(base_scheme_name.value)
-    if style_scheme.props.id in (MeldStyleScheme.dark.value, MeldStyleScheme.base.value):
+    base_schemes = (MeldStyleScheme.dark.value, MeldStyleScheme.base.value)
+    if style_scheme and style_scheme.props.id in base_schemes:
         style_scheme = base_style_scheme
 
     return base_style_scheme