Fix dynmap version being null when dynmap doesn't support the minecraft versio

- Fixes #69

src/main/kotlin/net/trivernis/chunkmaster/Chunkmaster.kt

@@ -9,6 +9,8 @@ import org.bstats.bukkit.Metrics
 import org.bukkit.plugin.java.JavaPlugin
 import org.bukkit.scheduler.BukkitTask
 import org.dynmap.DynmapAPI
+import java.lang.IllegalStateException
+import java.lang.NullPointerException
 
 class Chunkmaster : JavaPlugin() {
     lateinit var sqliteManager: SqliteManager
@@ -103,12 +105,16 @@ class Chunkmaster : JavaPlugin() {
     }
 
     private fun getDynmap(): DynmapAPI? {
+        return try {
             val dynmap = server.pluginManager.getPlugin("dynmap")
-        return if (dynmap != null && dynmap is DynmapAPI) {
+            if (dynmap != null && dynmap is DynmapAPI) {
                 logger.info(langManager.getLocalized("PLUGIN_DETECTED", "dynmap", dynmap.dynmapVersion))
                 dynmap
             } else {
                 null
             }
+        } catch (e: IllegalStateException) {
+            null
+        }
     }
 }