[pr #2637] recent versions of ecj double-close the classfile stream, causing corrupt classfiles

Would crash with java.lang.ClassFormatError: Extra bytes at the end of class file de/lomboktest/Application
Fixes https://github.com/mplushnikov/lombok-intellij-plugin/issues/969

figuring out the problem was the hard work - credits to @Rawi01 for discovering this

src/core/lombok/core/PostCompiler.java

@@ -28,6 +28,7 @@ import java.io.PrintWriter;
 import java.io.StringWriter;
 import java.util.Collections;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 public final class PostCompiler {
 	private PostCompiler() {/* prevent instantiation*/};
@@ -67,8 +68,17 @@ public final class PostCompiler {
 	
 	public static OutputStream wrapOutputStream(final OutputStream originalStream, final String fileName, final DiagnosticsReceiver diagnostics) throws IOException {
 		if (System.getProperty("lombok.disablePostCompiler", null) != null) return originalStream;
+		
+		// close() can be called more than once and should be idempotent, therefore, ensure we never transform more than once.
+		final AtomicBoolean closed = new AtomicBoolean();
+		
 		return new ByteArrayOutputStream() {
 			@Override public void close() throws IOException {
+				if (closed.getAndSet(true)) {
+					originalStream.close();
+					return;
+				}
+				
 				// no need to call super
 				byte[] original = toByteArray();
 				byte[] copy = null;