[meld/ci-fixes] filediff: Fix a minor flake8 complaint

[Kai Willadsen <kaiw src gnome org>]

commit 78bae2e96156af757285077a18fc526e55be89e7
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sat Aug 6 17:11:51 2022 +1000

    filediff: Fix a minor flake8 complaint
    
    This was a complaint about assert spacing, but we may as well make
    these actual checks.

 meld/filediff.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/meld/filediff.py b/meld/filediff.py
index 5a686c6d..f12d3601 100644
--- a/meld/filediff.py
+++ b/meld/filediff.py
@@ -970,9 +970,13 @@ class FileDiff(Gtk.VBox, MeldDoc):
 
     @with_focused_pane
     def action_delete_change(self, pane, *args):
+        if self.cursor.chunk is None:
+            return
+
         chunk = self.linediffer.get_chunk(self.cursor.chunk, pane)
-        assert(self.cursor.chunk is not None)
-        assert(chunk is not None)
+        if chunk is None:
+            return
+
         self.delete_chunk(pane, chunk)
 
     def _synth_chunk(self, pane0, pane1, line):