Fix #2564: Make sure lock is held in all AssemblyList ctors that modify it.

ILSpy/AssemblyList.cs

@@ -85,9 +85,13 @@ namespace ICSharpCode.ILSpy
 		/// </summary>
 		public AssemblyList(AssemblyList list, string newName)
 			: this(newName)
+		{
+			lock (lockObj)
 			{
 				this.assemblies.AddRange(list.assemblies);
 			}
+			this.dirty = false;
+		}
 
 		public event NotifyCollectionChangedEventHandler CollectionChanged {
 			add {