fix(option list): fix size when options cleared

Fix the OptionList size not updating correctly after clearing the
options.

Fixes #5728

Author: TomJGooding

src/textual/widgets/_option_list.py

@@ -759,8 +759,7 @@ def _get_option_render(self, option: Option, style: Style) -> list[Strip]:
 
     def _update_lines(self) -> None:
         """Update internal structures when new lines are added."""
-        if not self.options or not self.scrollable_content_region:
-            # No options -- nothing to
+        if not self.scrollable_content_region:
             return
 
         line_cache = self._line_cache

tests/snapshot_tests/__snapshots__/test_snapshots/test_option_list_size_when_options_cleared.svg

@@ -3915,3 +3915,23 @@ def action_remove_options(self) -> None:
                 option_list.remove_option_at_index(0)
 
     snap_compare(OptionListApp(), press=["x"])
+
+
+def test_option_list_size_when_options_cleared(snap_compare):
+    """Regression test for https://github.com/Textualize/textual/issues/5728
+
+    You should see the height of the OptionList has updated correctly after
+    its options are cleared.
+    """
+
+    class OptionListApp(App):
+        BINDINGS = [("x", "clear_options", "Clear options")]
+
+        def compose(self) -> ComposeResult:
+            yield OptionList(*[f"Option {n}" for n in range(30)])
+            yield Footer()
+
+        def action_clear_options(self) -> None:
+            self.query_one(OptionList).clear_options()
+
+    snap_compare(OptionListApp(), press=["x"])