Issue Description: Getting a NullPointerException in DynmapCore.java at 441 - Caused by null return from System.getenv("PATH")

• Dynmap Version: Dynmap-3.1-beta5-spigot
• Server Version: Paper version git-Paper-288 (MC: 1.16.4)
• Pastebin of Configuration.txt: irrelevant
• Server Host (if applicable): Bisect
• Pastebin of crashlogs or other relevant logs: https://pastebin.com/q4zBpYJB
• Other Relevant Data/Screenshots: Added an if statement to return null if System.getenv("PATH") returns null and it is working, just reporting the missing cwebp or dwebp modules rather than blowing up.
• Steps to Replicate: Remove (or secure) the PATH env variable.

[X] I have looked at all other issues and this is not a duplicate
[X] I have been able to replicate this

DynmapCore.zip

This is a duplicate of #3170