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

ILSpy/AssemblyList.cs

@@ -86,7 +86,11 @@ namespace ICSharpCode.ILSpy
 		public AssemblyList(AssemblyList list, string newName)
 			: this(newName)
 		{
-			this.assemblies.AddRange(list.assemblies);
+			lock (lockObj)
+			{
+				this.assemblies.AddRange(list.assemblies);
+			}
+			this.dirty = false;
 		}
 
 		public event NotifyCollectionChangedEventHandler CollectionChanged {