Fix: Settings window reads wrong variable for max_factory_spacing_percent

[S_N_C]

As explained in title, the settings window uses the value of max_factory_spacing when setting up the number box for max_factory_spacing_percent.

Fix is a one-liner, submitting a patch is probably overkill but whatever 

[prissi]

Since this is a manual setting, I though I intended it to set the actual distance in tiles. Thanks for noticing.

[jamespetts]

Thank you - incorporated into Experimental, too!