Auto merge of #16894 - bzbarsky:two-value-text-overflow, r=manishearth

Fix the two-value form of text-overflow to work in stylo

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix https://bugzilla.mozilla.org/show_bug.cgi?id=1365168

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16894)
<!-- Reviewable:end -->

components/style/properties/gecko.mako.rs

@@ -3626,9 +3626,7 @@ fn static_assert() {
         }
 
         self.clear_overflow_sides_if_string();
-        if v.second.is_none() {
-            self.gecko.mTextOverflow.mLogicalDirections = true;
-        }
+        self.gecko.mTextOverflow.mLogicalDirections = v.second.is_none();
 
         let SpecifiedValue { ref first, ref second } = v;
         let second = second.as_ref().unwrap_or(&first);