Fix copy constructors of Callback objects
Fix copy constructors of Callback objects

->move() operator was not touching unused data fields, therefore
leaving uninitialised data and failing the comparison.
Fixed by initialising all fields to zero before moving.

andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,mbedmicro/mbed,kjbracey-arm/mbed