shared/shell: Fix memory leak when parsing args

When running the command having mandatory arguments, memory leak occurs
as below:

  1 bytes in 1 blocks are definitely lost in loss record 2 of 184
     at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
     by 0x5679C99: strdup (strdup.c:42)
     by 0x13A976: cmd_exec (shell.c:327)
     by 0x13A976: menu_exec (shell.c:375)
     by 0x13AEA4: shell_exec (shell.c:418)
     by 0x13BBF1: rl_handler (shell.c:563)
     by 0x53C8D72: rl_callback_read_char (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x13ACE0: input_read (shell.c:1018)
     by 0x13C90A: watch_callback (io-glib.c:170)
     by 0x4E86E24: g_main_context_dispatch (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.5400.1)
     by 0x4E871EF: ??? (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.5400.1)
     by 0x4E87501: g_main_loop_run (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.5400.1)
     by 0x13D244: mainloop_run (mainloop-glib.c:73)

  7 bytes in 1 blocks are definitely lost in loss record 12 of 184
     at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
     by 0x5679C99: strdup (strdup.c:42)
     by 0x139EEA: strdelimit (util.c:991)
     by 0x13B66A: args_completion (shell.c:668)
     by 0x13B66A: menu_completion (shell.c:695)
     by 0x13B836: shell_completion (shell.c:723)
     by 0x53B98B6: ??? (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53B9A99: rl_complete_internal (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53B02EE: _rl_dispatch_subseq (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53B07B5: readline_internal_char (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53C8F84: rl_callback_read_char (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x13ACE0: input_read (shell.c:1018)
     by 0x13C90A: watch_callback (io-glib.c:170)

  9 bytes in 1 blocks are definitely lost in loss record 21 of 184
     at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
     by 0x5679C99: strdup (strdup.c:42)
     by 0x13B53F: args_completion (shell.c:654)
     by 0x13B53F: menu_completion (shell.c:695)
     by 0x13B836: shell_completion (shell.c:723)
     by 0x53B98B6: ??? (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53B9A99: rl_complete_internal (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53B02EE: _rl_dispatch_subseq (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53B07B5: readline_internal_char (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x53C8F84: rl_callback_read_char (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x13ACE0: input_read (shell.c:1018)
     by 0x13C90A: watch_callback (io-glib.c:170)
     by 0x4E86E24: g_main_context_dispatch (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.5400.1)

  9 bytes in 1 blocks are definitely lost in loss record 22 of 184
     at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
     by 0x5679CE9: strndup (strndup.c:43)
     by 0x13A9EB: cmd_exec (shell.c:301)
     by 0x13A9EB: menu_exec (shell.c:375)
     by 0x13AEA4: shell_exec (shell.c:418)
     by 0x13BBF1: rl_handler (shell.c:563)
     by 0x53C8D72: rl_callback_read_char (in /lib/x86_64-linux-gnu/libreadline.so.7.0)
     by 0x13ACE0: input_read (shell.c:1018)
     by 0x13C90A: watch_callback (io-glib.c:170)
     by 0x4E86E24: g_main_context_dispatch (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.5400.1)
     by 0x4E871EF: ??? (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.5400.1)
     by 0x4E87501: g_main_loop_run (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.5400.1)
     by 0x13D244: mainloop_run (mainloop-glib.c:73)
1 file changed