Fix possible crash when texture is NULL in the drop shadow cache.

Change-Id: I2142c55dbcfebcdf013a7f4ae04b266a60f5ce8a
diff --git a/libs/hwui/TextDropShadowCache.cpp b/libs/hwui/TextDropShadowCache.cpp
index 9d54277..2f7c7be 100644
--- a/libs/hwui/TextDropShadowCache.cpp
+++ b/libs/hwui/TextDropShadowCache.cpp
@@ -74,10 +74,10 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 void TextDropShadowCache::operator()(ShadowText& text, ShadowTexture*& texture) {
-    const uint32_t size = texture->width * texture->height;
-    mSize -= size;
-
     if (texture) {
+        const uint32_t size = texture->width * texture->height;
+        mSize -= size;
+
         glDeleteTextures(1, &texture->id);
         delete texture;
     }