Report 0 rowsDecoded for no rows (SkPngCodec interlaced)

src/codec/SkPngCodec.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 "SkBitmap.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 746 matching lines @@
         fDst = dst;
         fRowBytes = rowBytes;
         fLinesDecoded = 0;
     }
 
     SkCodec::Result decode(int* rowsDecoded) override {
         this->processData();
 
         // Now apply Xforms on all the rows that were decoded.
         if (!fLinesDecoded) {
+            if (rowsDecoded) {
+                *rowsDecoded = 0;
+            }
             return SkCodec::kIncompleteInput;
         }
         const int lastRow = fLinesDecoded + fFirstRow - 1;
         SkASSERT(lastRow <= fLastRow);
 
         // FIXME: For resuming interlace, we may swizzle a row that hasn't changed. But it
         // may be too tricky/expensive to handle that correctly.
         png_bytep srcRow = fInterlaceBuffer.get();
         const int sampleY = this->swizzler() ? this->swizzler()->sampleY() : 1;
         void* dst = fDst;
@@ skipping 524 matching lines @@
     SkCodec* outCodec = nullptr;
     if (read_header(streamDeleter.get(), chunkReader, &outCodec, nullptr, nullptr)) {
         // Codec has taken ownership of the stream.
         SkASSERT(outCodec);
         streamDeleter.release();
         return outCodec;
     }
 
     return nullptr;
 }