If a function starts with line number 0, don't try to check if a breakpoint...

If a function starts with line number 0, don't try to check if a breakpoint crossed function boundaries.

clang doesn't use line number 0 (to mean artifically generated code) very often, but swift does it
quite often.  We were rejecting all by line breakpoints in functions that started at line 0.  But that's
a special marker so we can just not do this test in that case.

llvm-svn: 339182