Corrected onModified calls for various nodes

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Nodes/PropertyNode.cs

                     return;
 
                 m_Exposed = value;
-                if (onModified != null)
-                {
-                    onModified(this, ModificationScope.Graph);
-                }
             }
         }
 

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Nodes/Vector2Node.cs

         public Vector2 value
         {
             get { return m_Value; }
-            set { m_Value = value; }
+            set
+            {
+                if (m_Value == value)
+                    return;
+
+                m_Value = value;
+
+                if (onModified != null)
+                    onModified(this, ModificationScope.Node);
+            }
         }
 
         public override void GeneratePropertyBlock(PropertyGenerator visitor, GenerationMode generationMode)

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Nodes/Vector3Node.cs

         public Vector3 value
         {
             get { return m_Value; }
-            set { m_Value = value; }
+            set
+            {
+                if (m_Value == value)
+                    return;
+
+                m_Value = value;
+
+                if (onModified != null)
+                    onModified(this, ModificationScope.Node);
+            }
         }
 
         public override void GeneratePropertyBlock(PropertyGenerator visitor, GenerationMode generationMode)

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Nodes/Vector4Node.cs

         public Vector4 value
         {
             get { return m_Value; }
-            set { m_Value = value; }
+            set
+            {
+                if (m_Value == value)
+                    return;
+
+                m_Value = value;
+
+                if (onModified != null)
+                    onModified(this, ModificationScope.Node);
+            }
         }
 
         public override void GeneratePropertyBlock(PropertyGenerator visitor, GenerationMode generationMode)