Fix gcc8 error about strncpy

With gcc8 we get the following error when stringop-truncation is on:

```
In function ‘_rotate_log_file’,
    inlined from ‘log_msg.part.2’ at src/log.c:201:17:
src/log.c:231:5: error: ‘strncpy’ output truncated before terminating nul copying as many bytes from a string as its length [-Werror=stringop-truncation]
     strncpy(log_file_new, log_file, len);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/log.c: In function ‘log_msg.part.2’:
src/log.c:228:18: note: length computed here
     size_t len = strlen(log_file);
                  ^~~~~~~~~~~~~~~~
```

Using memcpy instead of strncpy.

0 files changed, 0 insertions, 0 deletions