fix: 修复版本文件夹内不存在jar文件时启动器可能意外报错的问题

Author: ShirosakiMio

FCLCore/src/main/java/com/tungsten/fclcore/launch/DefaultLauncher.java

@@ -209,7 +209,7 @@ private CommandBuilder generateCommandLine() throws IOException {
         File jar = repository.getVersionJar(version);
         if (!jar.exists() || !jar.isFile()) {
             String inherits = version.getInheritsFrom();
-            if (!inherits.isEmpty()) {
+            if (inherits != null && !inherits.isEmpty()) {
                 jar = repository.getVersionJar(inherits);
             }
         }