Fix bug where an item was not added to the delta view of the sharing map

[danpoe]

The bug could appear when there are hash collisions between the keys stored in the sharing map.

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• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
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[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 13f792e).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/112106949

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: f82e08e).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/112109280