shared/shell: Fix memory leak of wordexp with we_offs

This sets the we_offs variable to zero before do wordfree(). Since it
frees from the elements of the we_wordv array pointed to by the we_offs
variable, memory leak occurs as below:

  101 bytes in 1 blocks are definitely lost in loss record 122 of 184
     at 0x4C2FA3F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
     by 0x4C31D84: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
     by 0x56E7CD2: w_addchar (wordexp.c:104)
     by 0x56E7CD2: parse_dquote (wordexp.c:2200)
     by 0x56E7CD2: wordexp (wordexp.c:2349)
     by 0x13A6A5: parse_args (shell.c:262)
     by 0x13A94D: cmd_exec (shell.c:313)
     by 0x13A94D: 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)

  117 (16 direct, 101 indirect) bytes in 1 blocks are definitely lost in loss record 125 of 184
     at 0x4C31D2F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
     by 0x56E81C3: w_addword (wordexp.c:182)
     by 0x56E81C3: wordexp (wordexp.c:2447)
     by 0x13A6A5: parse_args (shell.c:262)
     by 0x13B55A: args_completion (shell.c:656)
     by 0x13B55A: 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)
1 file changed