Fix for ImportDB.get_default(None)

Condition was swapped and avoided adding current folder as a search path
for db

lib/python/pyflyby/_importdb.py

@@ -284,7 +284,7 @@ def get_default(cls, target_filename: Union[Filename, str], /):
         target_path = Path(target_filename).resolve()
 
         parents: List[Path]
-        if not target_path.is_dir():
+        if target_path.is_dir():
             parents = [target_path]
         else:
             parents = []