fix: zero len put error when content length value not defined

Fixes #444. For some clients using chunked uploads with a zero
length file, the content length value from the request headers
was coming back as an empty string. If this happens, just set
it to "0" so that we can successfully parse this to int value.

s3api/controllers/base.go

@@ -909,6 +909,9 @@ func (c S3ApiController) PutActions(ctx *fiber.Ctx) error {
 
 	// Other headers
 	contentLengthStr := ctx.Get("Content-Length")
+	if contentLengthStr == "" {
+		contentLengthStr = "0"
+	}
 	bucketOwner := ctx.Get("X-Amz-Expected-Bucket-Owner")
 
 	grants := grantFullControl + grantRead + grantReadACP + granWrite + grantWriteACP