util, nb_dns: fix off-by-one bugs in strncpy() calls

Fortunately, these bugs had no effect because the following lines
overwrote the last character with a null byte.

src/util.h

@@ -512,7 +512,7 @@ inline void* safe_malloc(size_t size)
 
 inline char* safe_strncpy(char* dest, const char* src, size_t n)
 	{
-	char* result = strncpy(dest, src, n);
+	char* result = strncpy(dest, src, n-1);
 	dest[n-1] = '\0';
 	return result;
 	}