OpenLayers map on homepage may appear blank on new install

[Jeff McKenna]

• initially reported by @tchaddad
• honestly I once saw this happen during the 5.2.0 release candidate process
  • in my case, it only happened on my heavily used machine, with tons of tabs open, in Firefox (that was running a long time, weeks likely, without an update)
    • by "heavily used" I mean I was running the setup.exe installer over and over again into different ports and folders and tabs, and eventually one run caused a blank map in the OpenLayers map on MS4W's homepage (127.0.0.1)
  • clearing the browser cache didn't fix it
  • magically, I closed Firefox (hard restarted it) and I have never seen this issue since

Needs more research (and hopefully steps to replicate here). From quick research I notice other OpenLayers users with somewhat similar reports:

• ​https://github.com/openlayers/openlayers/issues/15839

This will be a tough one. Hmm. Any more findings @tchaddad??

Seems like some sort of memory issue.

Difficult to know yet if a change is needed inside the actual MapServer source code, or to MS4W's embedded OpenLayers code.