Prevent crash when setting up a stencil-based clip
Bug #8177690

Clear the layers before we setup the stencil to avoid dereferencing
the recently deleted rects.

Change-Id: I5dce5f965672f276f9490636d85b6018d3ab9422
diff --git a/libs/hwui/font/Font.cpp b/libs/hwui/font/Font.cpp
index 1afcb46..1a75ea8 100644
--- a/libs/hwui/font/Font.cpp
+++ b/libs/hwui/font/Font.cpp
@@ -189,7 +189,10 @@
     vOffset += glyph->mBitmapTop + height;
 
     SkPoint destination[4];
-    measure.getPosTan(x + hOffset + glyph->mBitmapLeft + halfWidth, position, tangent);
+    bool ok = measure.getPosTan(x + hOffset + glyph->mBitmapLeft + halfWidth, position, tangent);
+    if (!ok) {
+        ALOGW("The path for drawTextOnPath is empty or null");
+    }
 
     // Move along the tangent and offset by the normal
     destination[0].set(-tangent->fX * halfWidth - tangent->fY * vOffset,