fix(stats): apply union only if needed

The component sharing is rarely used so optimize for the case there is
no shared component at the expense of one additional (cheap) query in
case it is.

weblate/trans/models/project.py

@@ -564,9 +564,13 @@ def filter_access(qs):
 
         return self.get_child_components_filter(filter_access).order()
 
+    @cached_property
+    def has_shared_components(self) -> bool:
+        return self.shared_components.exists()
+
     def get_child_components_filter(self, filter_callback):
         own = filter_callback(self.component_set.defer_huge())
-        if self.shared_components.exists():
+        if self.has_shared_components:
             shared = filter_callback(self.shared_components.defer_huge())
             return own.union(shared)
         return own

weblate/utils/stats.py

@@ -1081,9 +1081,9 @@ def get_translate_url(self):
     @cached_property
     def translation_set(self):
         all_langs = self.language.translation_set.prefetch()
-        result = all_langs.filter(component__project=self.project).union(
-            all_langs.filter(component__links=self.project)
-        )
+        result = all_langs.filter(component__project=self.project)
+        if self.project.has_shared_components:
+            result = result.union(all_langs.filter(component__links=self.project))
         for item in result:
             item.is_shared = (
                 None