Linux: Improve debugging of pslist dump feature

volatility3/framework/plugins/linux/elfs.py

@@ -84,6 +84,7 @@ class Elfs(plugins.PluginInterface):
         )
 
         if not elf_object.is_valid():
+            vollog.debug("ELF object to be dumped is not valid")
             return None
 
         sections = {}

volatility3/framework/plugins/linux/pslist.py

@@ -142,6 +142,8 @@ class PsList(interfaces.plugins.PluginInterface):
                         file_output = str(file_handle.preferred_filename)
                         file_handle.close()
                     break
+            else:
+                file_output = "VMA start matching task start_code not found"
         return file_output
 
     def _generator(