fix stroke sub-hairline threshold

bug:7339943

Change-Id: I4051a03f4cd5bd2c313840208540601fb7a056e2
diff --git a/libs/hwui/PathRenderer.cpp b/libs/hwui/PathRenderer.cpp
index 5b55c2b..58d6cb8 100644
--- a/libs/hwui/PathRenderer.cpp
+++ b/libs/hwui/PathRenderer.cpp
@@ -215,7 +215,7 @@
     // alpha value (TODO: support different X/Y scale)
     float maxAlpha = 1.0f;
     if (halfStrokeWidth != 0 && inverseScaleX == inverseScaleY &&
-            halfStrokeWidth * inverseScaleX < 1.0f) {
+            halfStrokeWidth * inverseScaleX < 0.5f) {
         maxAlpha *= (2 * halfStrokeWidth) / inverseScaleX;
         halfStrokeWidth = 0.0f;
     }