change API contract: disallow zero-sized images or surfaces

src/image/SkSurface_Raster.cpp

Index: src/image/SkSurface_Raster.cpp
diff --git a/src/image/SkSurface_Raster.cpp b/src/image/SkSurface_Raster.cpp
index b221c130e5e6f735acbd6b2a6fe0f515970de829..2bac3f3156f998a7f4e757c339751fa9b3fc455a 100644
--- a/src/image/SkSurface_Raster.cpp
+++ b/src/image/SkSurface_Raster.cpp
@@ -39,6 +39,10 @@ private:
 ///////////////////////////////////////////////////////////////////////////////
 
 bool SkSurface_Raster::Valid(const SkImageInfo& info, size_t rowBytes) {
+    if (info.isEmpty()) {
+        return false;
+    }
+
     static const size_t kMaxTotalSize = SK_MaxS32;
 
     int shift = 0;