Issue 494: Fix error reporting in http state reader

pkg/iac/terraform/state/backend/http_reader.go

@@ -46,7 +46,11 @@ func (h *HTTPBackend) Read(p []byte) (n int, err error) {
 			return 0, errors.Errorf("error requesting HTTP(s) backend state: status code: %d", res.StatusCode)
 		}
 	}
-	return h.reader.Read(p)
+	read, err := h.reader.Read(p)
+	if err != nil {
+		return 0, err
+	}
+	return read, nil
 }
 
 func (h *HTTPBackend) Close() error {