Fix memcached return default on falsy values (#443)

Author: FormJani

django_prometheus/cache/backends/memcached.py

@@ -13,9 +13,10 @@ def get(self, key, default=None, version=None):
         cached = super().get(key, default=None, version=version)
         if cached is not None:
             django_cache_hits_total.labels(backend="memcached").inc()
-        else:
-            django_cache_misses_total.labels(backend="memcached").inc()
-        return cached or default
+            return cached
+
+        django_cache_misses_total.labels(backend="memcached").inc()
+        return default
 
 
 class PyLibMCCache(MemcachedPrometheusCacheMixin, memcached.PyLibMCCache):