pylibfdt: fix get_mem_rsv for newer Python versions

The test for get_mem_rsv fails on newer versions of Python with the
following error.

> Traceback (most recent call last):
>   File "/__w/dtc/dtc/tests/pylibfdt_tests.py", line 421, in testReserveMap
>     self.assertEqual([ 0xdeadbeef00000000, 0x100000],
> AssertionError: Lists differ: [16045690981097406464, 1048576] != [0, 16045690981097406464, 1048576]
>
> First differing element 0:
> 16045690981097406464
> 0
>
> Second list contains 1 additional elements.
> First extra element 2:
> 1048576
>
> - [16045690981097406464, 1048576]
> + [0, 16045690981097406464, 1048576]
> ?  +++

It appears this is because the PyTuple_GET_SIZE() function that was used
to build the fdt_get_mem_rsv() return value has changed. It now is
returning a non-zero value when it's passed an integer, which causes the
SWIG wrapper to append the returned arguments to the return error rather
then ignore them.

This is valid behaviour per Python's documentation, which says it will
"Return the size of the tuple p, which must be non-NULL and point to a
tuple; no error checking is performed"[1]. As passing an integer is not
a tuple, its return value is undefined.

Fix this issue on older and newer versions by avoiding
PyTuple_GET_SIZE() entirely. Always append the arguments to the list,
and instead use the wrapper python function to check the first argument
and then splice the last two arguments as the return value.

[1] https://docs.python.org/3/c-api/tuple.html#c.PyTuple_GET_SIZE

Signed-off-by: Brandon Maier <brandon.maier@collins.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

pylibfdt/libfdt.i

@@ -295,7 +295,9 @@ class FdtRo(object):
         Returns:
             Number of memory reserve-map records
         """
-        return check_err(fdt_get_mem_rsv(self._fdt, index), quiet)
+        val = fdt_get_mem_rsv(self._fdt, index)
+        check_err(val[0], quiet)
+        return val[1:]
 
     def subnode_offset(self, parentoffset, name, quiet=()):
         """Get the offset of a named subnode
@@ -1188,12 +1190,7 @@ typedef uint32_t fdt32_t;
 
 %typemap(argout) uint64_t * {
         PyObject *val = PyLong_FromUnsignedLongLong(*arg$argnum);
-        if (!result) {
-           if (PyTuple_GET_SIZE(resultobj) == 0)
-              resultobj = val;
-           else
-              resultobj = SWIG_Python_AppendOutput(resultobj, val);
-        }
+        resultobj = SWIG_Python_AppendOutput(resultobj, val);
 }
 
 %include "cstring.i"