修复在内容编辑页面，音视频无法播放的问题

Author: TruthHun88

controllers/StaticController.go

@@ -49,7 +49,7 @@ func (this *StaticController) Uploads() {
 			}
 		}
 
-		if utils.IsSignUsed(sign) {
+		if sign != "" && utils.IsSignUsed(sign) {
 			this.Abort("404")
 		}
 	}

go.mod

@@ -27,6 +27,7 @@ require (
 	github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646
 	github.com/russross/blackfriday v2.0.0+incompatible
 	github.com/satori/go.uuid v1.2.0 // indirect
+	github.com/shiena/ansicolor v0.0.0-20200904210342-c7312218db18 // indirect
 	github.com/smartystreets/goconvey v1.6.4 // indirect
 	github.com/stretchr/testify v1.6.1 // indirect
 	github.com/unknwon/com v1.0.1

go.sum

@@ -226,6 +226,8 @@ github.com/satori/go.uuid v1.2.0 h1:0uYX9dsZ2yD7q2RtLRtPSdGDWzjeM3TbMJP9utgA0ww=
 github.com/satori/go.uuid v1.2.0/go.mod h1:dA0hQrYB0VpLJoorglMZABFdXlWrHn1NEOzdhQKdks0=
 github.com/shiena/ansicolor v0.0.0-20151119151921-a422bbe96644 h1:X+yvsM2yrEktyI+b2qND5gpH8YhURn0k8OCaeRnkINo=
 github.com/shiena/ansicolor v0.0.0-20151119151921-a422bbe96644/go.mod h1:nkxAfR/5quYxwPZhyDxgasBMnRtBZd0FCEpawpjMUFg=
+github.com/shiena/ansicolor v0.0.0-20200904210342-c7312218db18 h1:DAYUYH5869yV94zvCES9F51oYtN5oGlwjxJJz7ZCnik=
+github.com/shiena/ansicolor v0.0.0-20200904210342-c7312218db18/go.mod h1:nkxAfR/5quYxwPZhyDxgasBMnRtBZd0FCEpawpjMUFg=
 github.com/shurcooL/sanitized_anchor_name v1.0.0 h1:PdmoCO6wvbs+7yrJyMORt4/BmY5IYyJwS/kOiWx8mHo=
 github.com/shurcooL/sanitized_anchor_name v1.0.0/go.mod h1:1NzhyTcUVG4SuEtjjoZeVRXNmyL/1OwPU0+IJeTBvfc=
 github.com/siddontang/go v0.0.0-20170517070808-cb568a3e5cc0/go.mod h1:3yhqj7WBBfRhbBlzyOC3gUxftwsU0u8gqevxwIHQpMw=