Fix extra line issues.

Author: Yuncong Zhang

Runtime/Resources/UIWidgets_canvas_strokeAlpha.shader

@@ -9,7 +9,7 @@ Shader "UIWidgets/canvas_strokeAlpha"
     SubShader {
         ZTest Always
         ZWrite Off
-        Blend [_SrcBlend] [_DstBlend]
+        Blend OneMinusDstAlpha One
 
         Stencil {
             Ref 128

Runtime/ui/renderer/common/geometry/path/path_cache.cs

@@ -641,10 +641,10 @@ public void computeFillMesh(float fringe, out bool convex) {
                     }
 
                     if (path.nstroke > 0) {
-                        strokeIndices.Add(path.nstroke - 1);
-                        strokeIndices.Add(path.nstroke - 2);
+                        strokeIndices.Add(path.istroke + path.nstroke - 1);
+                        strokeIndices.Add(path.istroke + path.nstroke - 2);
                         strokeIndices.Add(path.istroke);
-                        strokeIndices.Add(path.nstroke - 1);
+                        strokeIndices.Add(path.istroke + path.nstroke - 1);
                         strokeIndices.Add(path.istroke);
                         strokeIndices.Add(path.istroke + 1);
                         for (var j = 2; j < path.nstroke; j++) {