Fix an uninitialized variable bug that caused write_pmbr() to bogusly return an error value that made Write_Disk() abort.  While on the subject, improve the initialization of the error variable in read_gpt() and update_gpt() even though nothing was broken there.
Fix an uninitialized variable bug that caused write_pmbr() to bogusly
return an error value that made Write_Disk() abort.  While on the
subject, improve the initialization of the error variable in read_gpt()
and update_gpt() even though nothing was broken there.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase