Add argument docs and negative tests

Author: JimBobSquarePants

src/ImageSharp/ImageFrame{TPixel}.cs

@@ -173,6 +173,7 @@ internal ImageFrame(Configuration configuration, ImageFrame<TPixel> source)
         /// </summary>
         /// <param name="rowIndex">The row.</param>
         /// <returns>The <see cref="Span{TPixel}"/></returns>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when row index is out of range.</exception>
         public Span<TPixel> GetPixelRowSpan(int rowIndex)
         {
             Guard.MustBeGreaterThanOrEqualTo(rowIndex, 0, nameof(rowIndex));

src/ImageSharp/Image{TPixel}.cs

@@ -169,6 +169,7 @@ internal Image(Configuration configuration, ImageMetadata metadata, IEnumerable<
         /// </summary>
         /// <param name="rowIndex">The row.</param>
         /// <returns>The <see cref="Span{TPixel}"/></returns>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when row index is out of range.</exception>
         public Span<TPixel> GetPixelRowSpan(int rowIndex)
         {
             Guard.MustBeGreaterThanOrEqualTo(rowIndex, 0, nameof(rowIndex));

tests/ImageSharp.Tests/Image/LargeImageIntegrationTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
 using Xunit;
@@ -17,5 +18,15 @@ public void CreateAndResize(TestImageProvider<Rgba32> provider)
             image.Mutate(c => c.Resize(1000, 1000));
             image.DebugSave(provider);
         }
+
+        [Theory]
+        [WithBasicTestPatternImages(width: 10, height: 10, PixelTypes.Rgba32)]
+        public void GetSingleSpan(TestImageProvider<Rgba32> provider)
+        {
+            provider.LimitAllocatorBufferCapacity().InPixels(10);
+            using Image<Rgba32> image = provider.GetImage();
+            Assert.False(image.TryGetSinglePixelSpan(out Span<Rgba32> imageSpan));
+            Assert.False(image.Frames.RootFrame.TryGetSinglePixelSpan(out Span<Rgba32> imageFrameSpan));
+        }
     }
 }