[Backport] make directory absolute

AUTHORS.rst

@@ -20,6 +20,7 @@ answer newbie questions, and generally made taiga that much better:
 - Andrea Stagi <stagi.andrea@gmail.com>
 - Andrés Moya <andres.moya@kaleidos.net>
 - Andrey Alekseenko <al42and@gmail.com>
+- Bruno Clermont <bruno@robotinfra.com>
 - Chris Wilson <chris.wilson@aridhia.com>
 - David Burke <david@burkesoftware.com>
 - Hector Colina <hcolina@gmail.com>

taiga/base/storage.py

@@ -41,7 +41,7 @@ class FileSystemStorage(storage.FileSystemStorage):
         # Note that there is a race between os.path.exists and os.makedirs:
         # if os.makedirs fails with EEXIST, the directory was created
         # concurrently, and we can continue normally. Refs #16082.
-        directory = os.path.dirname(name)
+        directory = os.path.join(settings.MEDIA_ROOT, os.path.dirname(name))
         if not os.path.exists(directory):
             try:
                 if self.directory_permissions_mode is not None: