git-gui: clear the goto line input when hiding

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

lib/line.tcl

@@ -45,6 +45,7 @@ method show {} {
 
 method hide {} {
 	if {[visible $this]} {
+		$w.ent delete 0 end
 		focus $ctext
 		grid remove $w
 	}