Set the upper limit of the render threads slider to the number of log…

…ical cores (#1616)

chunky/src/java/se/llbit/chunky/ui/render/tabs/AdvancedTab.java

@@ -165,7 +165,7 @@ public PictureExportFormat fromString(String string) {
     });
     renderThreads.setName("Render threads");
     renderThreads.setTooltip("Number of rendering threads.");
-    renderThreads.setRange(1, 20);
+    renderThreads.setRange(1, Runtime.getRuntime().availableProcessors());
     renderThreads.clampMin();
     renderThreads.onValueChange(value -> {
       PersistentSettings.setNumRenderThreads(value);