Fix memcached return default on falsy values

When a falsy value is returned from cache via memcached backend, it returns None (the default) instead, of the cached value.

This is the same issue as with the Redis backend, which was fixed here:
1860549

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):