Fix a crash in strncpy/stpncpystrn

```
Core was generated by `scripts/mod/modpost -M -m -o Module.symvers -n -T modules.order vmlinux.o'.
Program terminated with signal SIGSEGV, Segmentation fault.
warning: 17     src/string/strlen.c: No such file or directory
(gdb) bt
```

> I think strncpy logic is broken: `__fh_size_t max_len_s = strlen(__s);` may try read past `size_t __n`.
> Create a buf without any trailing `\0`, do `strncpy(dest, buf, sizeof(buf));`, it should work, since `strncpy` will stop at `sizeof buf`
> but the current fority-headers implementation will do `strlen(buf)`, which will go boom when it is not terminated with \0

Reported-by: ncopa

1 files changed, 3 insertions, 1 deletions

diff --git a/tests/test_strncpy_dynamic_write.c b/tests/test_strncpy_dynamic_write.c
index 6af18a7..c779267 100644
--- a/tests/test_strncpy_dynamic_write.c
+++ b/tests/test_strncpy_dynamic_write.c
@@ -4,7 +4,9 @@
 
 int main(int argc, char** argv) {
   char buffer[8] = {0};
-  strncpy(buffer, "1234567", 5);
+  char src[] = {'A', 'B', 'C', 'D', 'E', 'F'};
+
+  strncpy(buffer, src, 5);
   puts(buffer);
 
   CHK_FAIL_START