Fix logic bugs related to e1e9427

[ewpatton]

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The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide

The details

Resolves

What Github issue does this resolve (please include link)?

Fixes #1373

Proposed Changes

Describe what this Pull Request does. Include screenshots if applicable.

This PR addresses #1373 by adding an else case in the event filter/merge mechanism to add events that collide with an existing hash but don't have paths for merging with existing events still get added to the event queue.

There is also a minor fix for an issue found with mutators where multiple move events are created and merged such that the resulting events are null, but still end up in the event queue and therefore the undo/redo stack. This causes UX problems because one may have to undo/redo twice.

Reason for Changes

Explain why these changes should be made. Include screenshots if applicable.

This commit is made to address #1373 where events that collided based on the hashing algorithm resulted in events being dropped.

Test Coverage

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Two tests were added to tests/jsunit/event_tests.js to test to ensure that the Scratch stackclick event doesn't get dropped following a click event and another to test that null events caused by merging are dropped.

Tested on:

• Desktop:

  • Chrome
  • Firefox
  • Safari
  • Opera
  • IE 10+
  • IE 11
  • EDGE

• Smartphone/Tablet/Chromebook (please complete the following information):

  • Device: [e.g. iPhone6]
  • OS: [e.g. iOS8.1]
  • Browser [e.g. stock browser, safari]
  • Version [e.g. 22]

Additional Information

Anything else we should know?

[rachel-fenichel]

Thanks.