fix ModMenu error if YACL isn't installed

src/main/java/one/oth3r/sit/ModMenu.java

@@ -21,6 +21,8 @@ public class ModMenu implements ModMenuApi {
     }
     @Override
     public ConfigScreenFactory<?> getModConfigScreenFactory() {
+        // return null if YACL isn't installed to not throw an error
+        if (!yaclCheck()) return screen -> null;
         return parent -> YetAnotherConfigLib.createBuilder().save(Config::save)
                 .title(Text.of("Sit!"))
                 .category(ConfigCategory.createBuilder()
@@ -198,4 +200,17 @@ public class ModMenu implements ModMenuApi {
                         .build())
                 .build().generateScreen(parent);
     }
+
+    /**
+     * check if YACL is installed by getting a class and seeing if it throws
+     * @return if YACL is installed
+     */
+    public static boolean yaclCheck() {
+        try {
+            Class.forName("dev.isxander.yacl3.platform.fabric.YACLPlatformImpl");
+            return true;
+        } catch (ClassNotFoundException e) {
+            return false;
+        }
+    }
 }