Fails with memory-only NUMA node

[srcshelton]

On a Raspberry Pi 4 with (fake) NUMA enabled, the sysfs contents are:

$ grep -i memtotal /sys/devices/system/node/node*/meminfo
/sys/devices/system/node/node0/meminfo:Node 0 MemTotal:        3949332 kB
/sys/devices/system/node/node1/meminfo:Node 1 MemTotal:        4111376 kB

$ grep '^.*$' /sys/devices/system/node/node*/cpulist
/sys/devices/system/node/node0/cpulist:0-3
/sys/devices/system/node/node1/cpulist:

... which causes (without pyperf available?):

$ sudo ./src/sysreport.py 
Traceback (most recent call last):
  File "/home/stuart/sysreport-main/./src/sysreport.py", line 1029, in <module>
    S = System()
        ^^^^^^^^
  File "/home/stuart/sysreport-main/./src/sysreport.py", line 271, in __init__
    self.system = cpulist.system()
                  ^^^^^^^^^^^^^^^^
  File "/home/stuart/sysreport-main/src/cpulist.py", line 924, in system
    g_system = System()
               ^^^^^^^^
  File "/home/stuart/sysreport-main/src/cpulist.py", line 604, in __init__
    self.discover()
  File "/home/stuart/sysreport-main/src/cpulist.py", line 716, in discover
    cpu_list = intmask_list(cpusetstr_mask(file_word(node + "/cpulist")))
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/stuart/sysreport-main/src/cpulist.py", line 102, in cpusetstr_mask
    m |= (1 << int(r))
               ^^^^^^
ValueError: invalid literal for int() with base 10: ''