add assert to resolve unckeched return, CID 997072

src/knot/conf/includes.c

@@ -14,6 +14,7 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <assert.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -94,7 +95,10 @@ static char *path_relative_to(const char *filename, const char *reference)
 	if (!result)
 		return NULL;
 
-	snprintf(result, result_len, "%.*s/%s", path_len, reference, filename);
+	int w;
+	w = snprintf(result, result_len, "%.*s/%s", path_len, reference, filename);
+	assert(w + 1 == result_len);
+
 	return result;
 }