themes kitten: Fix only the first custom theme file being loaded

Fixes #3938

docs/changelog.rst

@@ -18,6 +18,10 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
   by recency. ``recent:0`` matches the active window/tab, ``recent:1`` matches
   the previous window/tab and so on
 
+- themes kitten: Fix only the first custom theme file being loaded correctly
+  (:iss:`3938`)
+
+
 - A new :doc:`themes kitten </kittens/themes>` to easily change kitty themes.
 0.23.0 [2021-08-16]
 ----------------------

kittens/themes/collection.py

@@ -335,7 +335,7 @@ def load_from_dir(self, path: str) -> None:
                     d = parse_theme(name, raw)
                 except (Exception, SystemExit):
                     continue
-                t = Theme(lambda: raw)
+                t = Theme(raw.__str__)
                 t.apply_dict(d)
                 if t.name:
                     self.themes[t.name] = t