Use fake client flag to replace not conn check

The fake client flag was introduced in valkey-io#1063, we want
this to replace all !conn fake client checks.

Signed-off-by: Binbin <[email protected]>

src/networking.c

@@ -314,7 +314,9 @@ int prepareClientToWrite(client *c) {
      * is set. */
     if (c->flag.primary && !c->flag.primary_force_reply) return C_ERR;
 
-    if (!c->conn) return C_ERR; /* Fake client for AOF loading. */
+    /* Skip the fake client, such as the fake client for AOF loading. */
+    if (c->flag.fake) return C_ERR;
+    serverAssert(c->conn);
 
     /* Schedule the client to write the output buffers to the socket, unless
      * it should already be setup to do so (it has already pending data). */
@@ -4437,7 +4439,7 @@ int checkClientOutputBufferLimits(client *c) {
  *
  * Returns 1 if client was (flagged) closed. */
 int closeClientOnOutputBufferLimitReached(client *c, int async) {
-    if (!c->conn) return 0; /* It is unsafe to free fake clients. */
+    if (c->flag.fake) return 0; /* It is unsafe to free fake clients. */
     serverAssert(c->reply_bytes < SIZE_MAX - (1024 * 64));
     /* Note that c->reply_bytes is irrelevant for replica clients
      * (they use the global repl buffers). */

src/server.c

@@ -894,7 +894,7 @@ void updateClientMemoryUsage(client *c) {
 }
 
 int clientEvictionAllowed(client *c) {
-    if (server.maxmemory_clients == 0 || c->flag.no_evict || !c->conn) {
+    if (server.maxmemory_clients == 0 || c->flag.no_evict || c->flag.fake) {
         return 0;
     }
     int type = getClientType(c);