becdb: Safety around include of graphing library to prevent warnings
becdb: Safety around include of graphing library to prevent warnings

Newer versions of PHP issue warnings which go into the output stream when trying to
include a file which doesn't exist.  We change the way we include the graphing library
to get rid of these warnings.

Needed as part of migration to livegen.bristolenergy.coop.

bec-uk/bec_services,bec-uk/bec_services,bec-uk/bec_fault_mon,bec-uk/bec_fault_mon,bec-uk/bec_fault_mon,bec-uk/bec_services