Fix zero-width strokes still affecting the feathering color of boxes (#5485)

Author: emilk

crates/epaint/src/stroke.rs

@@ -161,10 +161,15 @@ where
 
 impl From<Stroke> for PathStroke {
     fn from(value: Stroke) -> Self {
-        Self {
-            width: value.width,
-            color: ColorMode::Solid(value.color),
-            kind: StrokeKind::default(),
+        if value.is_empty() {
+            // Important, since we use the stroke color when doing feathering of the fill!
+            Self::NONE
+        } else {
+            Self {
+                width: value.width,
+                color: ColorMode::Solid(value.color),
+                kind: StrokeKind::default(),
+            }
         }
     }
 }

crates/epaint/src/tessellator.rs

@@ -502,6 +502,8 @@ impl Path {
     /// Calling this may reverse the vertices in the path if they are wrong winding order.
     ///
     /// The preferred winding order is clockwise.
+    ///
+    /// The stroke colors is used for color-correct feathering.
     pub fn fill(&mut self, feathering: f32, color: Color32, stroke: &PathStroke, out: &mut Mesh) {
         fill_closed_path(feathering, &mut self.0, color, stroke, out);
     }
@@ -918,7 +920,7 @@ fn stroke_path(
 ) {
     let n = path.len() as u32;
 
-    if stroke.width <= 0.0 || stroke.color == ColorMode::TRANSPARENT || n < 2 {
+    if stroke.is_empty() || n < 2 {
         return;
     }