Fix the texture ID reuse issue in HWUI.

Issue: When the layer of previous frame is destroyed, it doesn't clear the
texture id in mBoundTextures[mTextureUnit], so in the next frame, if
glGenTexture returns same texture ID of the previous frame,
the new texture is not bound.

CRs-fixed: 671736

Change-Id: Ifc5fd2115fb1863b3c006ab14b0faabeaeb4eab4
diff --git a/libs/hwui/Layer.cpp b/libs/hwui/Layer.cpp
index bd371a3..987bf03 100644
--- a/libs/hwui/Layer.cpp
+++ b/libs/hwui/Layer.cpp
@@ -171,6 +171,7 @@
 }
 
 void Layer::clearTexture() {
+    caches.unbindTexture(texture.id);
     texture.id = 0;
 }