correctly set hasCo..LevelChanged with repeated setLevel calls

see Ant bug https://bz.apache.org/bugzilla/show_bug.cgi?id=62686
diff --git a/src/main/java/org/apache/commons/compress/archivers/zip/ZipArchiveOutputStream.java b/src/main/java/org/apache/commons/compress/archivers/zip/ZipArchiveOutputStream.java
index 584bb46..76aa0e1 100644
--- a/src/main/java/org/apache/commons/compress/archivers/zip/ZipArchiveOutputStream.java
+++ b/src/main/java/org/apache/commons/compress/archivers/zip/ZipArchiveOutputStream.java
@@ -875,7 +875,10 @@
             throw new IllegalArgumentException("Invalid compression level: "
                                                + level);
         }
-        hasCompressionLevelChanged = (this.level != level);
+        if (this.level == level) {
+            return;
+        }
+        hasCompressionLevelChanged = true;
         this.level = level;
     }