Make Interpreter::getStackTrace be able to generate the line number for the top callf...

Make Interpreter::getStackTrace be able to generate the line number for the top callframe if none is provided
https://bugs.webkit.org/show_bug.cgi?id=79407

Reviewed by Gavin Barraclough.

Outside of exception handling, we don't know what our source line number is.  This
change allows us to pass -1 is as the initial line number, and get the correct line
number in the resultant stack trace.  We can't completely elide the initial line
number (yet) due to some idiosyncrasies of the exception handling machinery.

* interpreter/Interpreter.cpp:
(JSC::getLineNumberForCallFrame):
(JSC):
(JSC::Interpreter::getStackTrace):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108681 268f45cc-cd09-0410-ab3c-d52691b4dbfc