Fix overflow caught by ASAN.

src/codec/SkBmpStandardCodec.h

Index: src/codec/SkBmpStandardCodec.h
diff --git a/src/codec/SkBmpStandardCodec.h b/src/codec/SkBmpStandardCodec.h
index d687eaad287a8c602219905c3810a9e3154f922a..829c89c103ea18a8e5c87d71c8e83572d9d0be4d 100644
--- a/src/codec/SkBmpStandardCodec.h
+++ b/src/codec/SkBmpStandardCodec.h
@@ -78,6 +78,7 @@ private:
     Result decodeIcoMask(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes);
 
     SkAutoTUnref<SkColorTable>          fColorTable;     // owned
+    // fNumColors is the number specified in the header, or 0 if not present in the header.
     const uint32_t                      fNumColors;
     const uint32_t                      fBytesPerColor;
     const uint32_t                      fOffset;