convert: avoid closing ui.fout in subversion code (issue5807)

Don't close 'fp' (= 'ui.fout') stream to prevent 'ValueError: I/O
operation on closed file' (Bug  #5807).

Regression of changeset 30261:6bed17ba00a1
(https://www.mercurial-scm.org/repo/hg/rev/6bed17ba00a1)

hgext/convert/subversion.py

@@ -149,7 +149,7 b' def get_log_child(fp, url, paths, start,'
         pickle.dump(str(inst), fp, protocol)
     else:
         pickle.dump(None, fp, protocol)
-    fp.close()
+    fp.flush()
     # With large history, cleanup process goes crazy and suddenly
     # consumes *huge* amount of memory. The output file being closed,
     # there is no need for clean termination.