hameg-hmo: Fix two compiler warnings (-Warray-bounds).

hameg-hmo: Fix two compiler warnings (-Warray-bounds).

  src/hardware/hameg-hmo/protocol.c: In function ‘hmo_scope_state_get’:
  src/hardware/hameg-hmo/protocol.c:1035:31: warning: array subscript 0 is above array bounds of ‘char *[0]’ [-Warray-bounds]
     g_free(logic_threshold_short[i]);
            ~~~~~~~~~~~~~~~~~~~~~^~~
  src/hardware/hameg-hmo/protocol.c:1035:31: warning: array subscript 0 is above array bounds of ‘char *[0]’ [-Warray-bounds]
  src/hardware/hameg-hmo/protocol.c:974:24: warning: array subscript 0 is above array bounds of ‘char *[0]’ [-Warray-bounds]
     logic_threshold_short[i] = g_strdup((*config->logic_threshold)[i]);
     ~~~~~~~~~~~~~~~~~~~~~^~~
  src/hardware/hameg-hmo/protocol.c:974:24: warning: array subscript 0 is above array bounds of ‘char *[0]’ [-Warray-bounds]