Workaround for some FileChannel problems

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

@@ -83,12 +83,23 @@ class FileNio extends FileBase {
     @Override
     public FileChannel truncate(long newLength) throws IOException {
         try {
+            long size = channel.size();
+            if (newLength < size) {
+                long pos = channel.position();
                 channel.truncate(newLength);
-            if (channel.position() > 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) {
             throw new IOException("read only");