message: Add friendlier error message when overwriting current file. Refs
  * Only the currently open capture can save over its file, other captures
  cannot overwrite it while it's in use.
diff: @@ -731,6 +731,14 @@ bool LiveCapture::saveCapture(Capture *cap)
  {
  QString path = m_Main->GetSavePath();
  + if(QString(m_Ctx.GetCaptureFilename()) == path)
  + {
  + RDDialog::critical(this, tr("Cannot save"), tr("Can't overwrite currently open capture at %1\n"
  + "Close the capture or save to another location.")
  + .arg(path));
  + return false;
  + }
  +
  // we copy the temp capture to the desired path, but the capture item remains referring to the
  // temp path.
  // This ensures that if the user deletes the saved path we can still open or re-save it.
  