exit computeFilters if filter width is zero

src/core/SkBitmapScaler.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 "SkBitmapScaler.h"
 #include "SkBitmapFilter.h"
 #include "SkConvolver.h"
@@ skipping 149 matching lines @@
 
     // Sum of the filter values for normalizing.
     // Distance from the center of the filter, this is the filter coordinate
     // in source space. We also need to consider the center of the pixel
     // when comparing distance against 'srcPixel'. In the 5x downscale
     // example used above the distance from the center of the filter to
     // the pixel with coordinates (2, 2) should be 0, because its center
     // is at (2.5, 2.5).
     float destFilterDist = (srcBegin + 0.5f - srcPixel) * clampedScale;
     int filterCount = SkScalarTruncToInt(srcEnd - srcBegin) + 1;
-    SkASSERT(filterCount > 0);
+    if (filterCount <= 0) {
+        // true when srcSize is equal to srcPixel - srcSupport; this may be a bug
+        return;
+    }
     filterValuesArray.reset(filterCount);
     float filterSum = fBitmapFilter->evaluate_n(destFilterDist, clampedScale, filterCount,
                                                 filterValuesArray.begin());
 
     // The filter must be normalized so that we don't affect the brightness of
     // the image. Convert to normalized fixed point.
     int fixedSum = 0;
     fixedFilterValuesArray.reset(filterCount);
     const float* filterValues = filterValuesArray.begin();
     SkConvolutionFilter1D::ConvolutionFixed* fixedFilterValues = fixedFilterValuesArray.begin();
@@ skipping 73 matching lines @@
     if (!result.peekPixels(&resultPM) || !Resize(resultPM, source, method)) {
         return false;
     }
 
     *resultPtr = result;
     resultPtr->lockPixels();
     SkASSERT(resultPtr->getPixels());
     return true;
 }