Fixes #11: Build error -Wstringop-truncation.

[jofemodo]

Replace strncpy by snprintf, that is a safer function and don't generate the compilation warning.

https://www.geeksforgeeks.org/why-strcpy-and-strncpy-are-not-safe-to-use/

[falkTX]

The strncpy usage is completely valid though...
In your changes, the 3rd set misses the "format", which I would say is funny seeing it build without errors (as it abuses snprintf)
I will fix this later on, changing a function just because of a compiler warning does not seem a good choice personally

[jofemodo]

I'm not missing the format but the specified format doesn't include any "%" replacement var ;-)

[jofemodo]

Regarding the use of strncpy, it's not valid in at less 3 calls because the input string length is not limited, so you can not be sure that the resulting destination string include a NULL terminating char, what will generate a buffer overflow.
So, if you specify a long device name or jack name as argument, you will cause the mod-ttymidi to segfault.

[falkTX]

This is now fixed