fix build error of pull request #5

It seems that pull request https://github.com/breckinloggins/ngtemplate/pull/5 can't build.

```
$ make
[  3%] Building C object libuseful/CMakeFiles/useful.dir/platform.c.o
[  7%] Building C object libuseful/CMakeFiles/useful.dir/hashtable.c.o
[ 11%] Building C object libuseful/CMakeFiles/useful.dir/list.c.o
[ 14%] Building C object libuseful/CMakeFiles/useful.dir/stringbuilder.c.o
[ 18%] Building C object libuseful/CMakeFiles/useful.dir/optin.c.o
Linking C static library libuseful.a
[ 18%] Built target useful
[ 22%] Building C object CMakeFiles/ngtemplate.dir/internal.c.o
[ 25%] Building C object CMakeFiles/ngtemplate.dir/stdenv.c.o
[ 29%] Building C object CMakeFiles/ngtemplate.dir/ngtemplate.c.o
Linking C static library libngtemplate.a
[ 29%] Built target ngtemplate
[ 33%] Building C object CMakeFiles/ngtembed.dir/ngtembed_tool.c.o
[ 37%] Building C object CMakeFiles/ngtembed.dir/ngtembed.c.o
ngtemplate/src/ngtembed.c: In function 'ngt_embed':
ngtemplate/src/ngtembed.c:53:8: error: 'ngt_template' has no member named 'template'
make[2]: *** [CMakeFiles/ngtembed.dir/ngtembed.c.o] Error 1
make[1]: *** [CMakeFiles/ngtembed.dir/all] Error 2
make: *** [all] Error 2
```