Fix "ERROR: no fileid for" in the testsuite.

If GDB has crashed then gdb_spawn_id still exists (although it does not work).
So my patch does not change anything.  And also currently it will leave the
stale gdbserver running anyway.

In general if gdb_spawn_id does not exist then send_gdb + gdb_expect just do
not make sense anyway.  So this patch just prevents the error in such case.

The killing of stale gdbserver could be improved multiple ways (also as
suggested by Pedro in the original thread) but that is IMO outside of the
scope of this patch.  Apparently if there is no good response from GDB then
gdb_finish() should try to call gdb_start just to kill that gdbserver, IIUC.

gdb/testsuite/
2014-02-16  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix "ERROR: no fileid for" in the testsuite.
	* lib/gdb.exp (gdb_finish): Check gdb_spawn_id.

Message-ID: <20140206205814.GA18495@host2.jankratochvil.net>
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