QmlDesigner: Remove unused local variables

Change-Id: I10d13161585fbe5c216fe939244f33fa27fb6336
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner: Validate model before accessing it

Change-Id: I0071e81309f9750006cab325d25c0602fb42a3f2
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlPuppet: Remove redundant null validations

Change-Id: I909119533646e0b29724212f764eb2685b683044
Reviewed-by: Marco Bubke <marco.bubke@digia.com>