Make dir/dbfilename/cluster-config-file reject empty string

Currently these configuration items allow typing empty strings,
but empty strings behave strangely.

Empty dir will fail in chdir with No such file or directory:
```
./src/valkey-server --dir ""

*** FATAL CONFIG FILE ERROR (Version 255.255.255) ***
Reading the configuration file, at line 2
>>> 'dir ""'
No such file or directory
```

Empty dbfilename will cause shutdown to fail since it will
always fail in rdb save:
```
./src/valkey-server --dbfilename ""

 * User requested shutdown...
 * Saving the final RDB snapshot before exiting.
 # Error moving temp DB file temp-19530.rdb on the final destination  (in server root dir /xxx/xxx/valkey): No such file or directory
 # Error trying to save the DB, can't exit.
 # Errors trying to shut down the server. Check the logs for more information.
```

Empty cluster-config-file will fail in clusterLockConfig:
```
./src/valkey-server --cluster-enabled yes --cluster-config-file ""

 Can't open  in order to acquire a lock: No such file or directory
```

With this patch, now we will just reject it in config set like:
```
*** FATAL CONFIG FILE ERROR (Version 255.255.255) ***
Reading the configuration file, at line 2
>>> 'xxx ""'
xxx can't be empty
```

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

src/config.c

@@ -2295,7 +2295,19 @@ static int isValidActiveDefrag(int val, const char **err) {
     return 1;
 }
 
+static int isValidClusterConfigFile(char *val, const char **err) {
+    if (!strcmp(val, "")) {
+        *err = "cluster-config-file can't be empty";
+        return 0;
+    }
+    return 1;
+}
+
 static int isValidDBfilename(char *val, const char **err) {
+    if (!strcmp(val, "")) {
+        *err = "dbfilename can't be empty";
+        return 0;
+    }
     if (!pathIsBaseName(val)) {
         *err = "dbfilename can't be a path, just a filename";
         return 0;
@@ -2658,6 +2670,10 @@ static int setConfigDirOption(standardConfig *config, sds *argv, int argc, const
         *err = "wrong number of arguments";
         return 0;
     }
+    if (!strcmp(argv[0], "")) {
+        *err = "dir can't be empty";
+        return 0;
+    }
     if (chdir(argv[0]) == -1) {
         *err = strerror(errno);
         return 0;
@@ -3061,7 +3077,7 @@ standardConfig static_configs[] = {
     createStringConfig("replica-announce-ip", "slave-announce-ip", MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.replica_announce_ip, NULL, NULL, NULL),
     createStringConfig("primaryuser", "masteruser", MODIFIABLE_CONFIG | SENSITIVE_CONFIG, EMPTY_STRING_IS_NULL, server.primary_user, NULL, NULL, NULL),
     createStringConfig("cluster-announce-ip", NULL, MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.cluster_announce_ip, NULL, NULL, updateClusterIp),
-    createStringConfig("cluster-config-file", NULL, IMMUTABLE_CONFIG, ALLOW_EMPTY_STRING, server.cluster_configfile, "nodes.conf", NULL, NULL),
+    createStringConfig("cluster-config-file", NULL, IMMUTABLE_CONFIG, ALLOW_EMPTY_STRING, server.cluster_configfile, "nodes.conf", isValidClusterConfigFile, NULL),
     createStringConfig("cluster-announce-hostname", NULL, MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.cluster_announce_hostname, NULL, isValidAnnouncedHostname, updateClusterHostname),
     createStringConfig("cluster-announce-human-nodename", NULL, MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.cluster_announce_human_nodename, NULL, isValidAnnouncedNodename, updateClusterHumanNodename),
     createStringConfig("syslog-ident", NULL, IMMUTABLE_CONFIG, ALLOW_EMPTY_STRING, server.syslog_ident, SERVER_NAME, NULL, NULL),