Handle null data in QRCodeTabsActivity.onActivityResult()

[grzesiek2010]

Closes #3945

What has been done to verify that this works as intended?

I reviewed implemented changes.

Why is this the best possible solution? Were any other approaches considered?

It is just a small fix, no other possible solution exist.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

I think it doesn't require testing.

Do we need any specific form for testing your changes? If so, please attach one.

No.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

No.

Before submitting this PR, please make sure you have:

• run ./gradlew checkAll and confirmed all checks still pass OR confirm CircleCI build passes and run ./gradlew connectedDebugAndroidTest locally.
• verified that any code or assets from external sources are properly credited in comments and/or in the about file.
• verified that any new UI elements use theme colors. UI Components Style guidelines

[seadowg]

Nice catch! It would be nice for this to be protected with a test but this code is moved around in #3933 so it probably makes sense for me to add a test there after dealing with the conflict.