Commit b1cc87cb656 ("msi: The line control has a height of exactly 2 device units.", 2007-12-16) open-coded the body of (msi_)dialog_add_control() inside dialog_line_control() modulo the height override.
Except the fixed height, line controls have nothing special compared to other controls. Thus, there is little merit in open-coding it.
Also, dialog_line_control() has bit-rotted over time; it already missed a few changes that were done to any other controls.
Fix this by just using dialog_add_control(). Also, add a special case logic just for line controls.