Fix the error when displaying algnments admin page

Fixes #296

django/meleager/admin/alignment.py

+from reversion_compare.admin import CompareVersionAdmin
+
 from django.contrib import admin
 from django.urls import reverse
 from django.utils.safestring import mark_safe
-from reversion_compare.admin import CompareVersionAdmin
 from meleager.models import Alignment
 
 
@@ -15,6 +16,8 @@ class AlignmentAdmin(CompareVersionAdmin):
 
     @admin.display(description="Passage")
     def first_passage_link(self, obj):
+        if not obj.text_1:
+            return ""
         passage = obj.text_1.passages.select_related("book").first()
         url = reverse(
             f"admin:{passage._meta.app_label}_{passage._meta.model_name}_change",