make gcc happy

[thrasibule]

The current code errors out with the new warning introduced with gcc 8.1.

error: ‘strncat’ output truncated before terminating nul copying as many bytes from a string as its length [-Werror=stringop-truncation]
   strncat(dst,ret,retlen);

[davisRoman]

@thrasibule I tried your patch with gcc 8.3 and it worked for me. Thank you!