Bump actions/download-artifact from 3 to 4.1.7 in /.github/workflows

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 3 to 4.1.7.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](https://github.com/actions/download-artifact/compare/v3...v4.1.7)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/ficus.yml

@@ -148,7 +148,7 @@ jobs:
         run: sudo apt-get update && sudo apt-get install -y cmake build-essential pax gcc g++ nasm bison bzip2 flex mtools texinfo libgmp-dev libmpfr-dev libmpc-dev xorriso
 
       - name: Download toolchain
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4.1.7
         with:
           name: toolchain-ficus
           path: ${{github.workspace}}

src/test/init.c

@@ -11,7 +11,11 @@
 
 void ls(char *dname) {
     while (dname[0] == ' ' && dname[0] != '\0') dname++;
-    DIR           *rfd = opendir(dname);
+    DIR *rfd = opendir(dname);
+    if (rfd == NULL) {
+        printf("Unknown directory: %s\n", dname);
+        return;
+    }
     struct dirent *cur = readdir(rfd);
     while (cur) {
         printf("%s\n", cur->d_name);
@@ -45,9 +49,11 @@ int main() {
         } else if (strcmp(line, "tasks") == 0) {
             print_tasks();
         } else {
-            if (fork() == 0)
+            if (fork() == 0) {
                 execve(line, 0, 0);
-            else
+                printf("Failed to start: %s\n", line);
+                return 0;
+            } else
                 wait(NULL);
         }
     }