Shell: Drop all the jobs after killing them in stop_all_jobs()

Author: https://github.com/alimpfard
Commit: a8c18f9fd2
Pull-request: https://github.com/SerenityOS/serenity/pull/3858

Shell/Shell.cpp

@@ -1585,6 +1585,8 @@ void Shell::stop_all_jobs()
                 perror("killpg(KILL)");
             }
         }
+
+        jobs.clear();
     }
 }