[Bug-apl] Assertion failure in evaluated input

[Kacper Gutowski]

When input to ⎕ is empty (just hit enter upon the prompt), it results
in assertion failure:


      ⎕
⎕:

items_allocated = 16
items[0] =
idx = 0

==============================================================================
Assertion failed: 0 && "Bad index"
in Function:      operator[]
in file:          Simple_string.hh:146

Call stack:

----------------------------------------
-- Stack trace at Simple_string.hh:146
----------------------------------------
0x7f6758ee9b45 __libc_start_main
0x43c7c5  main
0x55bc95   Workspace::immediate_execution(bool)
0x483165    Command::process_line()
0x47ca45     Command::do_APL_expression(UCS_string&)
0x48d795      Executable::execute_body() const
0x50c4d0       StateIndicator::run()
0x4b9901        Prefix::reduce_statements()
0x524bcc         Quad_Quad::resolve(Token&, bool)
0x4cd614          Bif_F1_EXECUTE::execute_statement(UCS_string&)
0x4bc476
0x44b740            do_Assert(char const*, char const*, char const*, int)
========================================

SI stack:

Depth:    0
Exec:     0x110c1c0
Safe ex:  no
Pmode:    ◊  ⎕
PC:       1 ENDL
Stat:     ⎕
err_code: 0x0
thrown:   at StateIndicator.cc:41
e_msg_1:  'No Error'
e_msg_2:  ''
e_msg_3:  ''


==============================================================================



-k