Update count_total_contacts to have a fallback

This was added for cases where the table has not yet been analyzed and the
estimate is not available... mainly in unit tests.

ctms/crud.py

@@ -59,12 +59,18 @@ def count_total_contacts(db: Session) -> int:
     This metadata is refreshed on `VACUUM` or `ANALYSIS` which
     is run regularly by default on our database instances.
     """
-    query = text(
-        "SELECT reltuples AS estimate "
-        "FROM pg_class "
-        f"where relname = '{Email.__tablename__}'"
-    )
-    result = db.execute(query).scalar()
+    result = db.execute(
+        text(
+            "SELECT reltuples AS estimate "
+            "FROM pg_class "
+            f"where relname = '{Email.__tablename__}'"
+        )
+    ).scalar()
+    if result is None or result < 0:
+        # Fall back to a full count if the estimate is not available.
+        result = db.execute(
+            text(f"SELECT COUNT(*) FROM {Email.__tablename__}")
+        ).scalar()
     if result is None:
         return -1
     return int(result)