Remove redundant !lit_utf8_iterator_is_eos (&source_str_iter) checks from lexer

[sand1k]

Refactor the lexer's code so that iterator is checked for EOS only in one place.

[egavrin]

Version: 17a5dd2

System:

Linux eg 4.2.0-18-generic #22-Ubuntu SMP Fri Nov 6 18:25:50 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Output:

ICE: Assertion '!lit_utf8_iterator_is_eos (&iter)' failed at /home/eg/dev/jr/jerry-core/parser/js/lexer.cpp(lexer_is_no_escape_sequences_in_token_string):1865.
Error: ERR_FAILED_INTERNAL_ASSERTION

Testcase:

// Copyrnse.

'use stricto

// C_pyrnsq.

'use strictI

// Copyrnse. Functionn f_0(){
    'use strictT

// Copyrnse.

'use strict)

// Copyrnse.

'use strict;

[LaszloLango]

Works on current master (91a0514).