check for null bitmap

Recent Skia driver addition of 8 bit src / 8 bit dst workaround
needs to check for a nullptr bitmap.

R==dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2255763002
diff --git a/core/fxge/skia/fx_skia_device.cpp b/core/fxge/skia/fx_skia_device.cpp
index 3effa0a..32e90e1 100644
--- a/core/fxge/skia/fx_skia_device.cpp
+++ b/core/fxge/skia/fx_skia_device.cpp
@@ -1463,7 +1463,7 @@
   SetBitmapPaint(pSource->IsAlphaMask(), argb, bitmap_alpha, blend_type,
                  &paint);
   // TODO(caryclark) Once Skia supports 8 bit src to 8 bit dst remove this
-  if (m_pBitmap->GetBPP() == 8 && pSource->GetBPP() == 8) {
+  if (m_pBitmap && m_pBitmap->GetBPP() == 8 && pSource->GetBPP() == 8) {
     SkMatrix inv;
     SkAssertResult(skMatrix.invert(&inv));
     for (int y = 0; y < m_pBitmap->GetHeight(); ++y) {