Update blur_filter.c (facebook#2621)

Summary:
unlock bitmap pixels if failed

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- [ ] Explain the **motivation** for making this change.
- [ ] Provide a **test plan** demonstrating that the code is solid.
- [ ] Match the **code formatting** of the rest of the codebase.
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## Motivation (required)

What existing problem does the pull request solve?
unlock bitmap pixels if failed

## Test Plan (required)

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[1]: https://medium.com/martinkonicek/what-is-a-test-plan-8bfc840ec171#.y9lcuqqi9
[2]: https://code.facebook.com/cla
[3]: http://circleci.com/gh/facebook/fresco
[4]: https://github.com/facebook/fresco/blob/master/CONTRIBUTING.md

Pull Request resolved: facebook#2621

Reviewed By: oprisnik

Differential Revision: D30337666

Pulled By: defHLT

fbshipit-source-id: 2d364f2b0b08b14983ce1e9c8b4e1b1cdbd911f1

native-filters/src/main/jni/filters/blur_filter.c

@@ -210,6 +210,7 @@ static void BlurFilter_iterativeBoxBlur(
   // pre-compute division table: speed-up by factor 5(!)
   uint8_t* div = (uint8_t*) malloc(256 * diameter * sizeof(uint8_t));
   if (!div) {
+    AndroidBitmap_unlockPixels(env, bitmap);
     safe_throw_exception(env, "BlurFilter_iterativeBoxBlur: Failed to allocate memory: div");
     return;
   }
@@ -230,6 +231,7 @@ static void BlurFilter_iterativeBoxBlur(
   pixel_t* tempRowOrColumn = (pixel_t*) malloc(max(w, h) * sizeof(pixel_t));
   if (!tempRowOrColumn) {
     free(div);
+    AndroidBitmap_unlockPixels(env, bitmap);
     safe_throw_exception(env, "BlurFilter_iterativeBoxBlur: Failed to allocate memory: tempRowOrColumn");
     return;
   }