rdbLoad(): rework code to save vertical space.

src/rdb.c

@@ -1067,10 +1067,8 @@ int rdbLoad(char *filename) {
     FILE *fp;
     rio rdb;
 
-    fp = fopen(filename,"r");
-    if (!fp) {
-        return REDIS_ERR;
-    }
+    if ((fp = fopen(filename,"r")) == NULL) return REDIS_ERR;
+
     rioInitWithFile(&rdb,fp);
     if (server.rdb_checksum)
         rdb.update_cksum = rioGenericUpdateChecksum;