Added a request for layout which was performed when the item
was hidden but not when the item was made visible again.


Change-Id: I7ed5ea1186d217c174cee81be4ea7d0c025b5a6e
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.ui/+/190978
Tested-by: Wim Jongman <wim.jongman@remainsoftware.com>
Tested-by: Lars Vogel <Lars.Vogel@vogella.com>
Reviewed-by: Wim Jongman <wim.jongman@remainsoftware.com>
Reviewed-by: Lars Vogel <Lars.Vogel@vogella.com>
Reviewed-by: Rolf Theunissen <rolf.theunissen@gmail.com>