DM: "wb" (binary mode) may matter on Windows

dm/DM.cpp

Index: dm/DM.cpp
diff --git a/dm/DM.cpp b/dm/DM.cpp
index b93f9d80788e200a2d0658a8d7b70e6c5fdeabc6..870b97a4efff97d3b68ea30f7f86504f827bda4a 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -495,7 +495,7 @@ static bool dump_png(SkBitmap bitmap, const char* path, const char* md5) {
     // We don't need bitmap anymore.  Might as well drop our ref.
     bitmap.reset();
 
-    FILE* f = fopen(path, "w");
+    FILE* f = fopen(path, "wb");
     if (!f) { return false; }
 
     png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);