Let do a refresh between project creation & external folder change.

Change-Id: Ia34c357ab3f98c4fcec35d7135a4610d3722d7e7
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/191122
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>