Vfx/fix/1327623 vfx recompiles for no change (#5518)

* Value comparison was not working because we are comparing objects

It was resulting in always recompiling the vfx even if the value had not changed

* Updated changelog

* NRE could happen if the model's current value is null

* Moved changelog entry from v12 to v13

Author: julienamsellem

com.unity.visualeffectgraph/CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Unexpected compilation error while modifying ShaderGraph exposed properties [Case 1361601](https://issuetracker.unity3d.com/product/unity/issues/guid/1361601/)
 - Compilation issue while using new SG integration and SampleTexture/SampleMesh [Case 1359391](https://issuetracker.unity3d.com/product/unity/issues/guid/1359391/)
 - Prevent VFX Graph compilation each time a property's min/max value is changed
+- Prevent vfx re-compilation in some cases when a value has not changed
 
 ## [12.0.0] - 2021-01-11
 ### Added

com.unity.visualeffectgraph/Editor/Models/VFXModel.cs

@@ -327,7 +327,7 @@ private bool SetSettingValueAndReturnIfChanged(string name, object value)
             }
 
             var currentValue = setting.value;
-            if (currentValue != value)
+            if (!currentValue?.Equals(value) ?? value != null)
             {
                 setting.field.SetValue(setting.instance, value);
                 OnSettingModified(setting);