Workaround for some FileChannel problems

h2/src/main/org/h2/store/fs/FilePathNio.java

@@ -83,11 +83,22 @@ class FileNio extends FileBase {
     @Override
     public FileChannel truncate(long newLength) throws IOException {
         try {
-            channel.truncate(newLength);
-            if (channel.position() > newLength) {
-                // looks like a bug in this FileChannel implementation, as the
-                // documentation says the position needs to be changed
-                channel.position(newLength);
+            long size = channel.size();
+            if (newLength < size) {
+                long pos = channel.position();
+                channel.truncate(newLength);
+                long newPos = channel.position();
+                if (pos < newLength) {
+                    // position should stay
+                    // in theory, this should not be needed
+                    if (newPos != pos) {
+                        channel.position(pos);
+                    }
+                } else if (newPos > newLength) {
+                    // looks like a bug in this FileChannel implementation, as the
+                    // documentation says the position needs to be changed
+                    channel.position(newLength);
+                }
             }
             return this;
         } catch (NonWritableChannelException e) {