Issue Description: Dynmap failed to start after update. Se log below.

• Dynmap Version: 3.7
• Server Version: forge 1.21.1
• Pastebin of Configuration.txt: original
• Server Host (if applicable): Selfhosted
• Pastebin of crashlogs or other relevant logs: https://pastebin.com/crashcausedbydynmap
• Other Relevant Data/Screenshots: No other plugins
• Steps to Replicate: Starting server after upgrade

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

[11:24:35] [Server thread/INFO]: [dynmap] Enabling dynmap v3.7-SNAPSHOT-948 [11:24:35] [Server thread/INFO]: [dynmap] Dynmap is disabled (unsupported platform) [11:24:35] [Server thread/ERROR]: Error occurred while enabling dynmap v3.7-SNAPSHOT-948 (Is it up to date?) java.lang.NullPointerException: Cannot invoke "org.dynmap.DynmapCore.disableCore()" because "this.core" is null at org.dynmap.bukkit.DynmapPlugin.onDisable(DynmapPlugin.java:1094) ~[?:?] at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:269) ~[spigot-api-1.21.1-R0.1-SNAPSHOT.jar:?] at org.dynmap.bukkit.DynmapPlugin.onEnable(DynmapPlugin.java:916) ~[?:?] at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:267) ~[spigot-api-1.21.1-R0.1-SNAPSHOT.jar:?] at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:342) ~[spigot-api-1.21.1-R0.1-SNAPSHOT.jar:?] at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:492) ~[spigot-api-1.21.1-R0.1-SNAPSHOT.jar:?] at org.bukkit.craftbukkit.v1_21_R1.CraftServer.enablePlugin(CraftServer.java:575) ~[spigot-1.21.1-R0.1-SNAPSHOT.jar:4295-Spigot-ca58122-7548afc] at org.bukkit.craftbukkit.v1_21_R1.CraftServer.enablePlugins(CraftServer.java:489) ~[spigot-1.21.1-R0.1-SNAPSHOT.jar:4295-Spigot-ca58122-7548afc] at net.minecraft.server.MinecraftServer.loadWorld0(MinecraftServer.java:641) ~[spigot-1.21.1-R0.1-SNAPSHOT.jar:4295-Spigot-ca58122-7548afc] at net.minecraft.server.MinecraftServer.loadLevel(MinecraftServer.java:426) ~[spigot-1.21.1-R0.1-SNAPSHOT.jar:4295-Spigot-ca58122-7548afc] at net.minecraft.server.dedicated.DedicatedServer.e(DedicatedServer.java:269) ~[spigot-1.21.1-R0.1-SNAPSHOT.jar:4295-Spigot-ca58122-7548afc] at net.minecraft.server.MinecraftServer.y(MinecraftServer.java:1017) ~[spigot-1.21.1-R0.1-SNAPSHOT.jar:4295-Spigot-ca58122-7548afc] at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:318) ~[spigot-1.21.1-R0.1-SNAPSHOT.jar:4295-Spigot-ca58122-7548afc] at java.base/java.lang.Thread.run(Thread.java:1583) [?:?]

Old version, try https://mikeprimm.com/dynmap/builds/dynmap/Dynmap-HEAD-forge-1.21.jar

Old version, try https://mikeprimm.com/dynmap/builds/dynmap/Dynmap-HEAD-forge-1.21.jar

What is old version? I updated both Buildtools and Dynmap today...

Old version, try https://mikeprimm.com/dynmap/builds/dynmap/Dynmap-HEAD-forge-1.21.jar

What is old version? I updated both Buildtools and Dynmap today...

Dynmap of course; yours is SNAPSHOT-948, the newest is 949.