Add default setting for initial zoomout validate option

src/main/resources/configuration.txt

@@ -186,6 +186,9 @@ saverestorepending: true
 # Zoom-out tile update period - how often to scan for and process tile updates into zoom-out tiles (in seconds)
 zoomoutperiod: 30
 
+# Control whether zoom out tiles are validated on startup (can be needed if zoomout processing is interrupted, but can be expensive on large maps)
+initial-zoomout-validate: true
+
 # Default delay on processing of updated tiles, in seconds.  This can reduce potentially expensive re-rendering
 # of frequently updated tiles (such as due to machines, pistons, quarries or other automation).  Values can
 # also be set on individual worlds and individual maps.