Fix IndexOutOfRangeException in FillRegionProcessor

[101100]

Prerequisites

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• I have verified that there are no overlapping pull-requests open
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Description

This is a fix for an issue that I have discovered as well as the reported issue #928. I have added two tests to illustrate the issue that fail on master as well as a possible fix.

The issue arises due to this code:

ImageSharp/src/ImageSharp.Drawing/Processing/Processors/Drawing/FillRegionProcessor{TPixel}.cs

Lines 99 to 112 in aac8eae

	int pointsFound = region.Scan(subPixel + offset, buffer, configuration);
	if (pointsFound == 0)
	{
	// nothing on this line, skip
	continue;
	}
	QuickSort.Sort(buffer.Slice(0, pointsFound));
	for (int point = 0; point < pointsFound; point += 2)
	{
	// points will be paired up
	float scanStart = buffer[point] - minX;
	float scanEnd = buffer[point + 1] - minX;

If pointsFound is odd (such as 3) and equal to the size of the buffer, the loop will go up to buffer.Length - 1, but that means that buffer[point + 1] will be out of bounds and cause an exception.

My solution was to add a second condition to the loop: point < buffer.Length - 1 Unfortunately, I don't know enough about the algorithm to know if this will result in an incorrect result.

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[codecov]

Codecov Report

Merging #964 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #964      +/-   ##
==========================================
+ Coverage   89.65%   89.66%   +0.01%     
==========================================
  Files        1097     1097              
  Lines       48542    48573      +31     
  Branches     3425     3425              
==========================================
+ Hits        43520    43553      +33     
+ Misses       4319     4317       -2     
  Partials      703      703

Impacted Files	Coverage Δ
.../Processors/Drawing/FillRegionProcessor{TPixel}.cs	97.61% <100%> (ø)	⬆️
...ageSharp.Tests/Drawing/FillRegionProcessorTests.cs	91.54% <100%> (+6.54%)	⬆️
...rawing/Processing/Extensions/DrawLineExtensions.cs	100% <0%> (+33.33%)	⬆️

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[codecov]

Codecov Report

Merging #964 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #964      +/-   ##
=========================================
+ Coverage   89.68%   89.7%   +0.01%     
=========================================
  Files        1097    1097              
  Lines       48474   48506      +32     
  Branches     3420    3420              
=========================================
+ Hits        43476   43510      +34     
+ Misses       4295    4293       -2     
  Partials      703     703

Impacted Files	Coverage Δ
.../Processors/Drawing/FillRegionProcessor{TPixel}.cs	97.61% <100%> (ø)	⬆️
...ageSharp.Tests/Drawing/FillRegionProcessorTests.cs	91.66% <100%> (+6.66%)	⬆️
...rawing/Processing/Extensions/DrawLineExtensions.cs	100% <0%> (+33.33%)	⬆️

---

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[JimBobSquarePants]

Thanks! @101100 !!

We'll have a good look at that asap. 👍

[tocsoft]

looks good. Thanks for the fix

[101100]

Thanks for the quick merge! I tested this in my project with the nightly build 1.0.0-dev002846 and it worked without an issue.