Incremental decode: only use subset for subsetting

src/codec/SkSampler.h

Index: src/codec/SkSampler.h
diff --git a/src/codec/SkSampler.h b/src/codec/SkSampler.h
index 00015585a11dda1fcf74e9ecc02ad9bec7f58662..e7bec0c035e4fad0694eccdf79dbc85f7bdb757b 100644
--- a/src/codec/SkSampler.h
+++ b/src/codec/SkSampler.h
@@ -8,6 +8,7 @@
 #define SkSampler_DEFINED
 
 #include "SkCodec.h"
+#include "SkCodecPriv.h"
 #include "SkTypes.h"
 
 class SkSampler : public SkNoncopyable {
@@ -37,11 +38,10 @@ public:
     /**
      *  Based on fSampleY, return whether this row belongs in the output.
      *
-     *  @param row Row of the image, starting with the first row used in the
-     *      output.
+     *  @param row Row of the image, starting with the first row in the subset.
      */
     bool rowNeeded(int row) const {
-        return row % fSampleY == 0;
+        return (row + get_start_coord(fSampleY)) % fSampleY == 0;
     }
 
     /**