MediaWiki writer: prevent triple `[[[`.

This confuses mediawiki's parser.  So we insert a `<nowiki/>`
no-op between a literal `[` and a link.  Closes #6119.

1 files changed, 10 insertions, 0 deletions

diff --git a/test/command/6119.md b/test/command/6119.md
new file mode 100644
index 000000000..6a0085e18
--- /dev/null
+++ b/test/command/6119.md
@@ -0,0 +1,10 @@
+```
+% pandoc -t mediawiki
+[[link](url)]
+
+[![image](url)]
+^D
+[<nowiki/>[[url|link]]]
+
+[<nowiki/>[[File:url|image]]]
+```