Correctly handle HTTP errors in RequestLogPolicy

The condition that tests the HTTP status code to decide whether or not to upgrade log severity never sees the 4xx and 5xx responses because they are encapsulated in a `StorageError`.

Addresses #214

azblob/zc_policy_request_log.go

@@ -62,15 +62,21 @@ func NewRequestLogPolicyFactory(o RequestLogOptions) pipeline.Factory {
 				logLevel, forceLog = pipeline.LogWarning, true
 			}
 
-			if err == nil { // We got a response from the service
-				sc := response.Response().StatusCode
-				if ((sc >= 400 && sc <= 499) && sc != http.StatusNotFound && sc != http.StatusConflict && sc != http.StatusPreconditionFailed && sc != http.StatusRequestedRangeNotSatisfiable) || (sc >= 500 && sc <= 599) {
-					logLevel, forceLog = pipeline.LogError, true // Promote to Error any 4xx (except those listed is an error) or any 5xx
+			var sc int
+			if err == nil { // We got a valid response from the service
+				sc = response.Response().StatusCode
+			} else { // We got an error, so we should inspect if we got a response
+				if r := err.(StorageError).Response(); r != nil {
+					sc = r.StatusCode
 				} else {
-					// For other status codes, we leave the level as is.
+					sc = -1
 				}
-			} else { // This error did not get an HTTP response from the service; upgrade the severity to Error
-				logLevel, forceLog = pipeline.LogError, true
+			}
+
+			if ((sc >= 400 && sc <= 499) && sc != http.StatusNotFound && sc != http.StatusConflict && sc != http.StatusPreconditionFailed && sc != http.StatusRequestedRangeNotSatisfiable) || (sc >= 500 && sc <= 599) || sc == -1 {
+				logLevel, forceLog = pipeline.LogError, true // Promote to Error any 4xx (except those listed is an error) or any 5xx
+			} else {
+				// For other status codes, we leave the level as is.
 			}
 
 			if shouldLog := po.ShouldLog(logLevel); forceLog || shouldLog {