Fix es action type

[yangyimincn]

修复es action类型为create时导致的panic

[yangyimincn]

当action为create时，会引发panic:

• | gohangout version 1.7.5
• | panic: interface conversion: interface {} is nil, not map[string]interface {}
• |
• | goroutine 46 [running]:
• | github.com/childe/gohangout/output.esGetRetryEvents(0xc00a4ee000, 0xc00a79c000, 0x120310, 0x1ffe00, 0xc003376110, 0x1ffe00, 0x0, 0x0, 0xc0006a6a00, 0x0, ...)
• | /tmp/gohangout-1.7.5/output/elasticsearch_output.go:155 +0xa9f
• | github.com/childe/gohangout/output.(*HTTPBulkProcessor).tryOneBulk(0xc0013420c0, 0xc004754150, 0x30, 0xc003376110, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
• | /tmp/gohangout-1.7.5/output/bulk_http.go:254 +0x8b5
• | github.com/childe/gohangout/output.(*HTTPBulkProcessor).innerBulk(0xc0013420c0, 0xc003376110)
• | /tmp/gohangout-1.7.5/output/bulk_http.go:166 +0x3d5
• | github.com/childe/gohangout/output.NewHTTPBulkProcessor.func1(0xc0013420c0)
• | /tmp/gohangout-1.7.5/output/bulk_http.go:102 +0xad
• | created by github.com/childe/gohangout/output.NewHTTPBulkProcessor
• | /tmp/gohangout-1.7.5/output/bulk_http.go:95 +0x2b4