Fix bug in sampled decodes

src/codec/SkSampledCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec.h"
 #include "SkCodecPriv.h"
 #include "SkMath.h"
@@ skipping 197 matching lines @@
                         dstHeight, 0);
                 return SkCodec::kIncompleteInput;
             }
             void* pixelPtr = pixels;
             for (int y = 0; y < dstHeight; y++) {
                 if (1 != fCodec->getScanlines(pixelPtr, 1, rowBytes)) {
                     fCodec->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
                             dstHeight, y + 1);
                     return SkCodec::kIncompleteInput;
                 }
-                int linesToSkip = SkTMin(sampleY - 1, dstHeight - y - 1);

[msarett, 2015/11/05 17:57:19]

I think the intent here was to not skip past the end of the image.

However, dstHeight - y - 1 doesn't make any sense.  I think what we want is:
srcHeight - fCurrScanline

Or, even better, we can just not skip on the last iteration.

-                if (!fCodec->skipScanlines(linesToSkip)) {
-                    fCodec->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
-                            dstHeight, y + 1);
-                    return SkCodec::kIncompleteInput;
+                if (y < dstHeight - 1) {
+                    if (!fCodec->skipScanlines(sampleY - 1)) {
+                        fCodec->fillIncompleteImage(info, pixels, rowBytes,
+                                options.fZeroInitialized, dstHeight, y + 1);
+                        return SkCodec::kIncompleteInput;
+                    }
                 }
                 pixelPtr = SkTAddOffset<void>(pixelPtr, rowBytes);
             }
             return SkCodec::kSuccess;
         }
         case SkCodec::kNone_SkScanlineOrder: {
             const int linesNeeded = subsetHeight - samplingOffsetY;
             SkAutoMalloc storage(linesNeeded * rowBytes);
             uint8_t* storagePtr = static_cast<uint8_t*>(storage.get());
 
@@ skipping 14 matching lines @@
                 // fCodec has already handled filling uninitialized memory.
                 return SkCodec::kIncompleteInput;
             }
             return SkCodec::kSuccess;
         }
         default:
             SkASSERT(false);
             return SkCodec::kUnimplemented;
     }
 }