Fix "No such file or directory" when connecting to ports >= 32768 (#1602)

* Fix `connect` for port numbers >=32768:

Since 5.0.0, using a high enough port number gives a "No such file or directory" error, because type casts treat high ports as -ve which awkwardly triggers the unix-socket-path behaviour.

* clean up guard condition

common.h

@@ -248,7 +248,7 @@ typedef struct fold_item {
 typedef struct {
     php_stream        *stream;
     zend_string       *host;
-    short             port;
+    unsigned short    port;
     zend_string       *auth;
     double            timeout;
     double            read_timeout;

redis.c

@@ -1005,6 +1005,10 @@ redis_connect(INTERNAL_FUNCTION_PARAMETERS, int persistent)
         port = 6379;
     }
 
+    if (port < 0) {
+        port = 0;
+    }
+
     redis = PHPREDIS_GET_OBJECT(redis_object, object);
     /* if there is a redis sock already we have to remove it */
     if (redis->sock) {