500 error on m2m facet detection

[simonw]

This may help debug:

diff --git a/datasette/facets.py b/datasette/facets.py
index 76d73e5..07a4034 100644
--- a/datasette/facets.py
+++ b/datasette/facets.py
@@ -499,11 +499,14 @@ class ManyToManyFacet(Facet):
                 "outgoing"
             ]
             if len(other_table_outgoing_foreign_keys) == 2:
-                destination_table = [
-                    t
-                    for t in other_table_outgoing_foreign_keys
-                    if t["other_table"] != self.table
-                ][0]["other_table"]
+                try:
+                    destination_table = [
+                        t
+                        for t in other_table_outgoing_foreign_keys
+                        if t["other_table"] != self.table
+                    ][0]["other_table"]
+                except IndexError:
+                    import pdb; pdb.pm()
                 # Only suggest if it's not selected already
                 if ("_facet_m2m", destination_table) in args:
                     continue

[simonw]

Part of #551