lib: fix off-by-one buffer allocation

Author: PrivacyIsARight

lib/package_alternatives.c

@@ -104,7 +104,7 @@ relpath(char *from, char *to)
 
 	for (up = -1, from--; from && *from; from = strchr(from + 1, '/'), up++);
 
-	rel = calloc(3 * up + strlen(p), 1);
+	rel = calloc(3 * up + strlen(p) + 1, 1);
 	if (!rel)
 		return NULL;