Currently ministat doesn't handle such use case:
```
[freefall ~w/freebsd/usr.bin/ministat (main)] ./ministat iguana - < chameleon
ministat: Cannot open -: No error: 0
```
Also, while porting to OpenBSD it was noted that handling of 'ministat - -' is also broken:
```
643 for (i = 0; i < nds; i++) {
644 setfilenames[i] = argv[i];
645 if (!strcmp(argv[i], "-"))
646 setfiles[0] = stdin;
647 else
648 setfiles[i] = fopen(argv[i], "r");
649 if (setfiles[i] == NULL)
650 err(2, "Cannot open %s", argv[i]);
651 }
```
on line 645 we check for '-' and if it matches we set setfiles[**0**] to stdin, in case of 'ministat - -' we don't set new element, and check setfiles[**1**] for NULL, and fail, on OpenBSD it leads to a crash, since array is un-initialized.
Proposed patch fixes these two cases.