Fix memory leak if a RedisCommand object were to be reused. That is, …

…a memory leak would have occured if the methods format() or formatArgv() were to be used more than once on the same object. This change simply ensures that currently allocated memory gets freed before new memory gets allocated. (sonic-net#392)

common/rediscommand.cpp

@@ -18,6 +18,12 @@ RedisCommand::~RedisCommand()
 
 void RedisCommand::format(const char *fmt, ...)
 {
+    if (temp != nullptr)
+    {
+        redisFreeCommand(temp);
+        temp = nullptr;
+    }
+
     va_list ap;
     va_start(ap, fmt);
     int len = redisvFormatCommand(&temp, fmt, ap);
@@ -31,6 +37,12 @@ void RedisCommand::format(const char *fmt, ...)
 
 void RedisCommand::formatArgv(int argc, const char **argv, const size_t *argvlen)
 {
+    if (temp != nullptr)
+    {
+        redisFreeCommand(temp);
+        temp = nullptr;
+    }
+
     int len = redisFormatCommandArgv(&temp, argc, argv, argvlen);
     if (len == -1) {
         throw std::bad_alloc();