javascript: fix translator comment extraction in C++-style comments

javascript: fix translator comment extraction in C++-style comments

* src/x-javascript.c (phase3_getc): Make sure to call comment_line_end
after parsing C++ style comment line.
Reported by Illimar Tambek at: <http://savannah.gnu.org/bugs/?40572>.

* tests/xgettext-javascript-1: Add a test to extract translator comments
from C++ style comment lines; only extract comments with
TRANSLATORS: tag.
* tests/xgettext-javascript-3: Only extract comments with TRANSLATORS:
tag.