[CLEANUP] acl, patterns: make use of my_strndup() instead of malloc+memcpy

This is simpler and more readable.
diff --git a/src/acl.c b/src/acl.c
index 0ded6bf..0634d5d 100644
--- a/src/acl.c
+++ b/src/acl.c
@@ -668,11 +668,8 @@
 		end = strchr(arg, ')');
 		if (!end)
 			goto out_free_expr;
-		arg2 = (char *)calloc(1, end - arg + 1);
-		if (!arg2)
+		arg2 = my_strndup(arg, end - arg);
 			goto out_free_expr;
-		memcpy(arg2, arg, end - arg);
-		arg2[end-arg] = '\0';
 		expr->arg_len = end - arg;
 		expr->arg.str = arg2;
 	}
diff --git a/src/pattern.c b/src/pattern.c
index 5afd068..63bae2b 100644
--- a/src/pattern.c
+++ b/src/pattern.c
@@ -397,9 +397,7 @@
 
 	if (end != endw) {
 		expr->arg_len = end - endw - 2;
-		expr->arg = malloc(expr->arg_len + 1);
-		expr->arg = memcpy(expr->arg, endw + 1, expr->arg_len);
-		expr->arg[expr->arg_len] = '\0';
+		expr->arg = my_strndup(endw + 1, expr->arg_len);
 	}
 
 	for (*idx += 1; *(str[*idx]); (*idx)++) {