Text area flicker fix (#4334)

Author: darrenburns

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Fixed a crash in `TextArea` when undoing an edit to a selection the selection was made backwards https://github.com/Textualize/textual/issues/4301
 - Fixed issue with flickering scrollbars https://github.com/Textualize/textual/pull/4315
+- Fixed issue where narrow TextArea would repeatedly wrap due to scrollbar appearing/disappearing https://github.com/Textualize/textual/pull/4334
 - Fix progress bar ETA not updating when setting `total` reactive https://github.com/Textualize/textual/pull/4316
 
 ### Changed 

src/textual/widgets/_text_area.py

@@ -688,7 +688,8 @@ def _watch_indent_width(self) -> None:
         self.scroll_cursor_visible()
 
     def _watch_show_vertical_scrollbar(self) -> None:
-        self._rewrap_and_refresh_virtual_size()
+        if self.wrap_width:
+            self._rewrap_and_refresh_virtual_size()
         self.scroll_cursor_visible()
 
     def _watch_theme(self, theme: str) -> None: