Protct the ECAL modules in the case of too many channels

[fwyzard]

Currently, the ECAL uncalibrated and rechit producers allocate a fixed-size buffer for the rechits, configurable via python.

If the number of channels to be converted is larger than the size, the modules should avoid using more memory than it is available.

Possible options:

• dynamically extend the buffer
• truncate the reconstructed rechits to the available memory (and print a LogError)
• throw an exception