Do not try the same (command, wraps) pair more than once when completing

This prevents runaway wrap chains. Fixes #5638.

tests/checks/wraps.fish

@@ -0,0 +1,29 @@
+#RUN: %fish %s
+# Validate some things about command wrapping.
+
+# This tests that we do not trigger a combinatorial explosion - see #5638.
+# Ensure it completes successully.
+complete -c testcommand --wraps "testcommand x "
+complete -c testcommand --wraps "testcommand y "
+complete -c testcommand --no-files -a normal
+complete -C'testcommand '
+# CHECK: normal
+
+# We get the same completion twice. TODO: fix this.
+# CHECK: normal
+
+
+# This tests that a call to complete from within a completion doesn't trigger
+# wrap chain explosion - #5638 again.
+function testcommand2_complete
+    set -l tokens (commandline -opc) (commandline -ct)
+    set -e tokens[1]
+    echo $tokens 1>&2
+    complete -C"$tokens"
+end
+
+complete -c testcommand2 -x -a "(testcommand2_complete)"
+complete -c testcommand2 --wraps "testcommand2 from_wraps "
+complete -C'testcommand2 explicit '
+# CHECKERR: explicit
+# CHECKERR: from_wraps explicit