fix: don't make overlays truthy when they just contain formats declaration

Author: vberlier

beet/library/base.py

@@ -1093,7 +1093,6 @@ def __bool__(self) -> bool:
         return (
             any(self.values())
             or self.extra.keys() > {"pack.mcmeta"}
-            or (self.overlay_parent is not None and self.supported_formats is not None)
             or (self.overlay_parent is None and bool(self.overlays))
         )
 

tests/test_data_pack.py

@@ -603,6 +603,7 @@ def test_overlay():
     b = p.overlays.setdefault(
         "b", supported_formats={"min_inclusive": 16, "max_inclusive": 17}
     )
+    assert not b
     assert b.supported_formats == {"min_inclusive": 16, "max_inclusive": 17}
     assert p.mcmeta.data == {
         "pack": {"pack_format": 18, "description": ""},
@@ -627,6 +628,7 @@ def test_overlay():
     c["demo:thing"] = Function()
     p.overlays["c"] = c
 
+    assert c
     assert c.overlay_name == "c"
     assert c.overlay_parent is p
     assert dict(p.list_files()) == {