Investigate inbound writes with malformed lengths with respect to actual data size

[Scottapotamas]

UI correctly sends a incorrectly encoded message. Micro decodes it into the buffer, and decides to write it over the local variable.

We know the data isn't formed correctly, so check the following edges are safe:

• [x] Data to write is less than the size of the full variable
• [x] Data to write is longer than we expect
• [x] Data to write + an offset is going to OOB
• [x] Data to write + offset doesn't OOB