s3: CopyObject return http Status 400 Bad Request for non-existing source

fix https://github.com/chrislusf/seaweedfs/issues/2306

weed/s3api/s3api_object_copy_handlers.go

@@ -33,11 +33,13 @@ func (s3a *S3ApiServer) CopyObjectHandler(w http.ResponseWriter, r *http.Request
 		entry, err := s3a.getEntry(dir, name)
 		if err != nil {
 			s3err.WriteErrorResponse(w, s3err.ErrInvalidCopySource, r)
+			return
 		}
 		entry.Extended = weed_server.SaveAmzMetaData(r, entry.Extended, isReplace(r))
 		err = s3a.touch(dir, name, entry)
 		if err != nil {
 			s3err.WriteErrorResponse(w, s3err.ErrInvalidCopySource, r)
+			return
 		}
 		writeSuccessResponseXML(w, CopyObjectResult{
 			ETag:         fmt.Sprintf("%x", entry.Attributes.Md5),
@@ -51,6 +53,13 @@ func (s3a *S3ApiServer) CopyObjectHandler(w http.ResponseWriter, r *http.Request
 		s3err.WriteErrorResponse(w, s3err.ErrInvalidCopySource, r)
 		return
 	}
+	srcPath := util.FullPath(fmt.Sprintf("%s/%s%s", s3a.option.BucketsPath, srcObject, srcObject))
+	dir, name := srcPath.DirAndName()
+	_, err = s3a.getEntry(dir, name)
+	if err != nil {
+		s3err.WriteErrorResponse(w, s3err.ErrInvalidCopySource, r)
+		return
+	}
 
 	if srcBucket == dstBucket && srcObject == dstObject {
 		s3err.WriteErrorResponse(w, s3err.ErrInvalidCopyDest, r)