fix(parser): avoid panic after asm lock prefix

[ShiroKSH]

Summary

• prevent the parser from indexing an empty token after an x86 lock prefix
• add a parser-error regression fixture for a truncated inline-assembly block

Root cause

After parsing lock, the parser advances to EOF for truncated input and indexed the empty token literal to check an instruction suffix. This crashed the compiler instead of reporting a syntax error.

Validation

• ./vnew -silent vlib/v/compiler_errors_test.v
• ./vnew -silent test vlib/v/parser/
• ./vnew -silent test vlib/encoding/base58/
• ./vnew -silent test vlib/encoding/binary/

[medvednikov]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep it up!

Reviewed commit: 99f5011f9d

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