Only clone header comments once

Author: garydgregory

src/main/java/org/apache/commons/csv/CSVPrinter.java

@@ -114,8 +114,9 @@ public CSVPrinter(final Appendable appendable, final CSVFormat format) throws IO
         this.format = format.copy();
         // TODO: Is it a good idea to do this here instead of on the first call to a print method?
         // It seems a pain to have to track whether the header has already been printed or not.
-        if (format.getHeaderComments() != null) {
-            for (final String line : format.getHeaderComments()) {
+        final String[] headerComments = format.getHeaderComments();
+        if (headerComments != null) {
+            for (final String line : headerComments) {
                 this.printComment(line);
             }
         }