Perfect coverage for sortfilter.

Mark an area of sortfilter with `#pragma no coverage` and add it to
perfect_files.

qutebrowser/completion/models/sortfilter.py

@@ -135,8 +135,8 @@ class CompletionFilterModel(QSortFilterProxyModel):
 
         for col in self.srcmodel.columns_to_filter:
             idx = self.srcmodel.index(row, col, parent)
-            if not idx.isValid():
-                # No entries in parent model
+            if not idx.isValid():  # pragma: no cover
+                # this is a sanity check not hit by any test case
                 continue
             data = self.srcmodel.data(idx)
             if not data:

scripts/dev/check_coverage.py

@@ -150,6 +150,8 @@ PERFECT_FILES = [
 
     ('tests/unit/completion/test_models.py',
         'qutebrowser/completion/models/base.py'),
+    ('tests/unit/completion/test_sortfilter.py',
+        'qutebrowser/completion/models/sortfilter.py'),
 
 ]