Make the DefaultScriptService lazy

This is actually required because the script languages want to have
a ScriptService injected by the context, and if we initialize the
script languages while initializing the ScriptService, the context
won't know the latter yet...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix NullPointerException in ScriptInfo

We actually *want* the reader to be null in certain circumstances...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'script-service-fixes'

Two fixes to make the script service play nicely with Fiji's legacy mode.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>