Fix a crash in jit.c

A user at Mozilla pointed out a crash in jit.c.  In his situation, an
inferior using the JIT API exec'd an executable that did not use it.
This caused an assertion failure when jit.c:free_objfile_data called
delete_breakpoint with NULL.

This patch fixes the problem in the obvious way.  New test case
included.

gdb/ChangeLog
2018-12-28  Tom Tromey  <tom@tromey.com>

	* jit.c (free_objfile_data): Only delete breakpoint if non-null.

gdb/testsuite/ChangeLog
2018-12-28  Tom Tromey  <tom@tromey.com>
	    Simon Marchi <simark@simark.ca>

	* gdb.base/jit-exec.exp: New file.
	* gdb.base/jit-exec.c: New file.
	* gdb.base/jit-execd.c: New file.

1 files changed, 22 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/jit-execd.c b/gdb/testsuite/gdb.base/jit-execd.c
new file mode 100644
index 0000000..6afe539
--- /dev/null
+++ b/gdb/testsuite/gdb.base/jit-execd.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+main (int argc, char **argv)
+{
+  return 0;
+}