exec_shell: prevent ".: applet not found" error when SHELL env is not set.
When SHELL env is not set, it cause xstrdup(NULL) be executed, and result in weird error message ".: applet not found" instead of /bin/sh being used.
exec_shell: prevent ".: applet not found" error when SHELL env is not set.
When SHELL env is not set, it cause xstrdup(NULL) be executed, and result in weird error message ".: applet not found" instead of /bin/sh being used.