Exception when opening project mulitple times (#164)

System.IO.IOException: The process cannot access the file 'C:\Users\(...)\Desktop\Project.simp' because it is being used by another process.

at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)

at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)

at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy)

at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access)

at SoftwareIdeasModeler.ProjectXml.SimXmlWriter.Save(String fileName)

at SoftwareIdeasModeler.MainForm.SaveToFile(String filename, Boolean isMultiFile)

at SoftwareIdeasModeler.MainForm.SaveFile()

at SoftwareIdeasModeler.MainForm.saveToolStripMenuItem_Click(Object sender, EventArgs e)

at System.Windows.Forms.ToolStripItem.RaiseEvent(Object key, EventArgs e)

at System.Windows.Forms.ToolStripMenuItem.OnClick(EventArgs e)

at System.Windows.Forms.ToolStripItem.HandleClick(EventArgs e)

at System.Windows.Forms.ToolStripMenuItem.ProcessCmdKey(Message& m, Keys keyData)

at System.Windows.Forms.ToolStripManager.ProcessShortcut(Message& m, Keys shortcut)

at System.Windows.Forms.Form.ProcessCmdKey(Message& msg, Keys keyData)

at SoftwareIdeasModeler.MainForm.ProcessCmdKey(Message& msg, Keys keyData)

at System.Windows.Forms.Control.ProcessCmdKey(Message& msg, Keys keyData)

at System.Windows.Forms.Control.ProcessCmdKey(Message& msg, Keys keyData)

at System.Windows.Forms.ContainerControl.ProcessCmdKey(Message& msg, Keys keyData)

at System.Windows.Forms.Form.ProcessCmdKey(Message& msg, Keys keyData)

at System.Windows.Forms.Control.ProcessCmdKey(Message& msg, Keys keyData)

at System.Windows.Forms.ContainerControl.ProcessCmdKey(Message& msg, Keys keyData)

at System.Windows.Forms.Control.PreProcessMessage(Message& msg)

at System.Windows.Forms.Control.PreProcessControlMessageInternal(Control target, Message& msg)

at System.Windows.Forms.Application.ThreadContext.PreTranslateMessage(MSG& msg)