fix for Retional.FromDouble(0)

Author: Tigran

src/ImageSharp/Primitives/LongRational.cs

@@ -153,6 +153,10 @@ public static LongRational FromDouble(double value, bool bestPrecision)
         double df = numerator / (double)denominator;
         double epsilon = bestPrecision ? double.Epsilon : .000001;
 
+        if(val < epsilon) {
+            return new LongRational(0, 1);
+        }
+
         while (Math.Abs(df - val) > epsilon)
         {
             if (df < val)
@@ -201,11 +205,6 @@ public LongRational Simplify()
             return this;
         }
 
-        if (this.Numerator == 0)
-        {
-            return new LongRational(0, 1);
-        }
-
         if (this.Numerator == this.Denominator)
         {
             return new LongRational(1, 1);

src/ImageSharp/Primitives/Rational.cs

@@ -74,11 +74,6 @@ public Rational(double value, bool bestPrecision)
 
         this.Numerator = (uint)rational.Numerator;
         this.Denominator = (uint)rational.Denominator;
-        
-        if(this.Numerator == 0 && this.Denominator == 0) 
-        {
-            this.Denominator = 1;
-        }
     }
 
     /// <summary>

tests/ImageSharp.Tests/Numerics/RationalTests.cs

@@ -41,6 +41,18 @@ public void AreNotEqual()
         Assert.True(first != second);
     }
 
+    /// <summary>
+    /// Tests the correct FromDouble(0).
+    /// </summary>
+    [Fact]
+    public void FromDouble0Non0Denominator()
+    {
+        var r = Rational.FromDouble(0);
+
+        Assert.Equal(0, r.Numerator);
+        Assert.Equal(1, r.Denominator);
+    }
+
     /// <summary>
     /// Tests whether the Rational constructor correctly assign properties.
     /// </summary>