Incorrect RotatingFileHandler closing

[fabregas]

In RotatingFileHandler.Close() when inputChanSize > 0 1 sending to exitChan.
RotatingFileHandler.loop() receives 1 from exitChan and returns.
In this case some log records can be ignored in inputChan channel.

This issue sometimes catches by the test:
--- FAIL: TestRotatingFileHandler_AppendWithoutBackup (0.00s)
Error Trace: handler_rotating_file_test.go:89
Error: Not equal:
expected: 0x3a98
actual: 0x3a34

[hhkbp2]

@fabregas Well done! The PR is merged.