[lines_issue.pdf](https://github.com/mozilla/pdf.js/files/3441553/lines_issue.pdf)

Configuration:
- Chrome (latest)
- Mac Os X Mojac
- PDF.js version: latest (reproduced on pdf.js demo page)

Steps to reproduce the problem:
1. Open attached pdf in pdf.js demo viewer
2. Please note that thin line in the middle is not affected by gradient, but it should be (see screenshot below taken from Mac Os X Preview)

What is the expected behavior? (add screenshot)

![image](https://user-images.githubusercontent.com/430887/62041871-5d375a00-b205-11e9-9811-97c1643ae5b9.png)

What went wrong? (add screenshot)

![image](https://user-images.githubusercontent.com/430887/62041851-51e42e80-b205-11e9-97a3-5a1ef1b20245.png)

*
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import {
  FONT_IDENTITY_MATRIX,
  IDENTITY_MATRIX,
  ImageKind,
  info,
  IsLittleEndianCached,
  isNum,
  OPS,
  shadow,
  TextRenderingMode,
  unreachable,
  Util,
  warn,
} from "../shared/util.js";
import { getShadingPatternFromIR, TilingPattern } from "./pattern_helper.js";
const MIN_FONT_SIZE = 16;
const MAX_FONT_SIZE = 100;
const MAX_GROUP_SIZE = 4096;
const COMPILE_TYPE3_GLYPHS = true;
const MAX_SIZE_TO_COMPILE = 1000;
const FULL_CHUNK_HEIGHT = 16;
const LINEWIDTH_SCALE_FACTOR = 1.000001;
function addContextCurrentTransform(ctx) {