fix(subprocess): return EMPTY before marking when the /proc scan collected nothing

Jenkins DeusData#95 failed in lint-cppcheck (ctunullpointer): when readdir
returned no usable entries, procs stayed NULL and was passed to
cbm_linux_probe_mark_tree, which calls qsort on it. A zero count made
that harmless at runtime, but passing NULL to qsort is undefined.

The probe now returns CBM_PROC_TREE_RSS_EMPTY directly when nothing was
collected, matching the result the loop would have produced.
`scripts/lint.sh --ci` and the subprocess suite (61 pass) pass locally.

Author: ngallodev

src/foundation/subprocess.c

@@ -948,6 +948,10 @@ static cbm_proc_tree_rss_status_t cbm_subprocess_tree_rss_platform(cbm_subproces
         cbm_free(CBM_MEM_CLASS_OTHER, procs);
         return CBM_PROC_TREE_RSS_ERROR;
     }
+    if (!procs || count == 0) {
+        cbm_free(CBM_MEM_CLASS_OTHER, procs);
+        return CBM_PROC_TREE_RSS_EMPTY;
+    }
 
     cbm_linux_probe_mark_tree(procs, count, process->pgid);
     uint64_t total = 0;