NewClient() bug if first call fails

**Describe the bug**

I have a connection timeout problem, the default one second timeout is too short to allow the sidecar to be ready, so my first call to NewClient fails. Any subsequent call won't have a chance to make a good connection after that.

if the first call of dapr.NewClient fails, it returns the correct error, and daprClient is nil, which is ok.
```go
daprClient, err = dapr.NewClient()
```
if I call it a second time after some delay, I will get daprClient==nil and err==nil, which is false. as daprClient is nil, it should retry a new connection and give the correct error for the new connection.

**To Reproduce**
if dapr.NewClient fails each time, you won't get an error, and you won't get a chance to retry a new connection in each iteration
```go
var daprClient dapr.Client
var err error

for i := 0; i < 3; i++ {
time.Sleep(time.Second * 3)
daprClient, err = dapr.NewClient()
if err != nil {
logger.WithError(err).WithField("i", i).Warn("create dapr client loop")
} else {
break
}
}
if err != nil {
logger.WithError(err).Error("create dapr client")
return
}
```

**Expected behavior**

if NewClient fails, it should retry to connect on next call and return a correct error, and not use doOnce.Do inconditionally.

Search the Go SDK for NewClient and its doOnce usage, then read the connection initialization path. Reproduce the failed-first-call sequence with the supplied retry loop and verify that each failed call returns the current connection error instead of nil; a later successful call should still return a client.

Written by the indexing model from the issue text.