The JSF com.sun.faces.facelets.tag.jsf.ComponentSupport in 2.2.7
started using FacesContext#isPostBack to check if a new component
tree is being built prior to attempting to find a child component.
In Web Flow where we redirect prior to rendering, and hence lose
the value of isPostback (because ResponseStateManagerImpl no longer
finds the parameter with the view state), it causes components to
be re-created and lose their local values.
This change overrides isPostback in FlowFacesContext in order to
return true in cases where the UIViewRoot has been restored from
flash scope and is fully built.
Issue: SWF-1645
2aa99ec0d0