[ob/pushed] Fix crash with stepi, no debug info, and "set debug infrun 1"

[Pedro Alves <pedro@palves.net>]

A stepi in a function without debug info with "set debug infrun 1"
crashes GDB since commit c8353d682f69 (gdb/infrun: some extra infrun
debug print statements), due to a reference to
"tp->current_symtab->filename" when tp->current_symtab is null.

This commit adds the missing null check.  The output in this case
becomes:

  [infrun] set_step_info: symtab = <null>, line = 0, step_frame_id = {stack=0x7fffffffd980,code=0x0000000000456c30,!special}, step_stack_frame_id = {stack=0x7fffffffd980,code=0x0000000000456c30,!special}

Change-Id: I5171a9d222bc7e15b9dba2feaba7d55c7acd99f8
---
 gdb/infrun.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index bc6521c8ec6..104c29abf0a 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -4180,7 +4180,8 @@ set_step_info (thread_info *tp, struct frame_info *frame,
 
   infrun_debug_printf
     ("symtab = %s, line = %d, step_frame_id = %s, step_stack_frame_id = %s",
-     tp->current_symtab->filename, tp->current_line,
+     tp->current_symtab != nullptr ? tp->current_symtab->filename : "<null>",
+     tp->current_line,
      tp->control.step_frame_id.to_string ().c_str (),
      tp->control.step_stack_frame_id.to_string ().c_str ());
 }

base-commit: da729c5ccde6eeccae539cbe51a285bc84769b3d
-- 
2.26.2