Optimize JarEntry construction

This commit avoids calling the underlying ZipEntry.setExtra() method
that is not very inline friendly in cases where there is no extra
information to be set.

See gh-16620

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/CentralDirectoryFileHeader.java

@@ -153,6 +153,10 @@ final class CentralDirectoryFileHeader implements FileHeader {
 		return this.extra;
 	}
 
+	public boolean hasExtra() {
+		return this.extra.length > 0;
+	}
+
 	public AsciiBytes getComment() {
 		return this.comment;
 	}

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarEntry.java

@@ -56,7 +56,9 @@ class JarEntry extends java.util.jar.JarEntry implements FileHeader {
 		setComment(header.getComment().toString());
 		setSize(header.getSize());
 		setTime(header.getTime());
-		setExtra(header.getExtra());
+		if (header.hasExtra()) {
+			setExtra(header.getExtra());
+		}
 	}
 
 	AsciiBytes getAsciiBytesName() {