Fix assertion in RegExp parser to correctly expect stack overflow.

Fix assertion in RegExp parser to correctly expect stack overflow.

Advance() always checks for stack overflow. If stack indeed overflowed,
current() would hold the kEndMarker. ParseOctalLiteral does not expect
this in the assertion, which causes assertion failure.

R=mvstanton@chromium.org
BUG=350865
LOG=N

Committed: https://code.google.com/p/v8/source/detail?r=19764

[mvstanton, 2014-03-10 15:49:19]

lgtm

[Yang, 2014-03-10 15:52:18]

Committed patchset #1 manually as r19764 (presubmit successful).