Fix Sysinfo FieldOrder

Fixes: #1027

Author: dbwiddis

CHANGES.md

@@ -11,6 +11,7 @@ Features
 Bug Fixes
 ---------
 * [#1025](https://github.com/java-native-access/jna/pull/1025): Restore java 6 compatibility and introduce animal-sniffer to prevent regressions - [@matthiasblaesing](https://github.com/matthiasblaesing).
+* [#1028](https://github.com/java-native-access/jna/pull/1028): Fix Linux LibC.Sysinfo FieldOrder - [@dbwiddis](https://github.com/dbwiddis).
 
 Release 5.0.0
 =============

contrib/platform/src/com/sun/jna/platform/linux/LibC.java

@@ -89,8 +89,8 @@ protected List<Field> getFieldList() {
         @Override
         protected List<String> getFieldOrder() {
             List<String> fieldOrder = new ArrayList<String>(super.getFieldOrder());
-            if (PADDING_SIZE > 0) {
-                fieldOrder.add("_f");
+            if (PADDING_SIZE == 0) {
+                fieldOrder.remove("_f");
             }
             return fieldOrder;
         }

src/com/sun/jna/Structure.java

@@ -1061,7 +1061,10 @@ protected List<Field> getFields(boolean force) {
         if (fieldOrder.size() != flist.size() && flist.size() > 1) {
             if (force) {
                 throw new Error("Structure.getFieldOrder() on " + getClass()
-                                + " does not provide enough names [" + fieldOrder.size()
+                                + (fieldOrder.size() < flist.size() 
+                                    ? " does not provide enough" 
+                                    : " provides too many")
+                                + " names [" + fieldOrder.size()
                                 + "] ("
                                 + sort(fieldOrder)
                                 + ") to match declared fields [" + flist.size()