Don't send a depth of "None" to the server when graph walker supports shallow.

Ideally this would have a test, but we don't have good tests for shallow anyway. :-/

Fixes #747

NEWS

@@ -1,5 +1,8 @@
 0.19.16	UNRELEASED
 
+ * Don't send "deepen None" to server if graph walker
+   supports shallow. (Jelmer Vernooij, #747)
+
 0.19.15	2020-01-26
 
  * Properly handle files that are just executable for the

dulwich/client.py

@@ -641,8 +641,9 @@ class GitClient(object):
                     "depth")
             for sha in graph_walker.shallow:
                 proto.write_pkt_line(COMMAND_SHALLOW + b' ' + sha + b'\n')
-            proto.write_pkt_line(COMMAND_DEEPEN + b' ' +
-                                 str(depth).encode('ascii') + b'\n')
+            if depth is not None:
+                proto.write_pkt_line(COMMAND_DEEPEN + b' ' +
+                                     str(depth).encode('ascii') + b'\n')
             proto.write_pkt_line(None)
             if can_read is not None:
                 (new_shallow, new_unshallow) = _read_shallow_updates(proto)