优化 GetTask 中 ByteArrayOutputStream 的初始大小 (#4209)

HMCLCore/src/main/java/org/jackhuang/hmcl/task/GetTask.java

@@ -60,9 +60,10 @@ public final class GetTask extends FetchTask<String> {
 
     @Override
     protected Context getContext(URLConnection connection, boolean checkETag, String bmclapiHash) {
-        return new Context() {
-            final ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        int length = connection.getContentLength();
+        final var baos = new ByteArrayOutputStream(length <= 0 ? 8192 : length);
 
+        return new Context() {
             @Override
             public void write(byte[] buffer, int offset, int len) {
                 baos.write(buffer, offset, len);