Better add test for != too, in case someone changes the != implementation

Author: tmilnthorp

UnitsNet.Tests/BaseDimensionsTests.cs

@@ -101,6 +101,11 @@ public void InequalityOperatorsWorkAsExpected()
 
             Assert.True(baseDimensions2 != null);
             Assert.True(null != baseDimensions2);
+
+            BaseDimensions nullBaseDimensions1 = null;
+            BaseDimensions nullBaseDimensions2 = null;
+
+            Assert.False(nullBaseDimensions1 != nullBaseDimensions2);
         }
 
         [Fact]

UnitsNet.Tests/BaseUnitsTests.cs

@@ -129,6 +129,11 @@ public void InequalityOperatorIsImplementedCorrectly()
 
             Assert.True(baseUnits1 != null);
             Assert.True(null != baseUnits1);
+
+            BaseUnits nullBaseUnits1 = null;
+            BaseUnits nullBaseUnits2 = null;
+
+            Assert.False(nullBaseUnits1 != nullBaseUnits2);
         }
 
         [Fact]

UnitsNet.Tests/UnitSystemTests.cs

@@ -146,6 +146,11 @@ public void InequalityOperatorIsImplementedCorrectly()
 
             Assert.True(unitSystem1 != null);
             Assert.True(null != unitSystem1);
+
+            UnitSystem nullUnitSystem1 = null;
+            UnitSystem nullUnitSystem2 = null;
+
+            Assert.False(nullUnitSystem1 != nullUnitSystem2);
         }
 
         [Fact]