python: check return value of Python object functions (RHBZ#1406906)

Verify the returned values of Python Object constructor functions
are not NULL before adding them to a collection.

This is particularly relevant when constructing Unicode strings in
Python 3 as they will return NULL if non UTF-8 characters are present.

Signed-off-by: Matteo Cafasso <noxdafox@gmail.com>

python/t/test830RHBZ1406906.py

@@ -0,0 +1,57 @@
+# libguestfs Python bindings
+# Copyright (C) 2017 Red Hat Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+import os
+import sys
+import shutil
+import tempfile
+import unittest
+
+import guestfs
+
+
+class Test830RHBZ1406906(unittest.TestCase):
+    def setUp(self):
+        self.tempdir = tempfile.mkdtemp()
+
+    def tearDown(self):
+        shutil.rmtree(self.tempdir)
+
+    def test_rhbz1406906(self):
+        g = guestfs.GuestFS(python_return_dict=True)
+
+        g.add_drive_scratch(512 * 1024 * 1024)
+        g.launch()
+
+        g.part_disk("/dev/sda", "mbr")
+        g.mkfs("ext4", "/dev/sda1")
+        g.mount("/dev/sda1", "/")
+
+        self.assertEqual(g.find("/"), ['lost+found'])
+
+        # touch file with illegal unicode character
+        non_utf8_fname = "\udcd4"
+        open(os.path.join(self.tempdir, non_utf8_fname), "w").close()
+
+        g.copy_in(self.tempdir, "/")
+
+        if sys.version_info >= (3, 0):
+            with self.assertRaises(UnicodeDecodeError):
+                g.find("/")  # segfault here on Python 3
+        elif sys.version_info >= (2, 0):
+            self.assertTrue(
+                any(path for path in g.find("/") if non_utf8_fname in path))