Fix regression in "commands"

Pedro pointed out a regression in "commands", where trying to clear a
breakpoint's command list would fail:

    (top-gdb) commands
    Type commands for breakpoint(s) 3, one per line.
    End with a line saying just "end".
    >end
    No breakpoints specified.
    (top-gdb)

I believe the bug was introduced by my patch that changes
counted_command_line to be a shared_ptr.  This causes the problem
because now the counted_command_line in commands_command_1 can be NULL,
whereas previously it never could be.

After some discussion, we agreed to simply remove the error case from
commands_command_1.

2017-12-07  Tom Tromey  <tom@tromey.com>

	PR breakpoints/22511:
	* breakpoint.c (commands_command_1): Don't throw an exception when
	no commands have been read.

2017-12-07  Tom Tromey  <tom@tromey.com>

	* gdb.base/break.exp: Add test for empty "commands".

1 files changed, 12 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/break.exp b/gdb/testsuite/gdb.base/break.exp
index 96e2f35003..87db2dc0d3 100644
--- a/gdb/testsuite/gdb.base/break.exp
+++ b/gdb/testsuite/gdb.base/break.exp
@@ -854,3 +854,15 @@ gdb_test_no_output "set \$foo=81.5" \
 gdb_test "break $srcfile:\$foo" \
     "Convenience variables used in line specs must have integer values.*" \
     "set breakpoint via non-integer convenience variable disallowed"
+
+
+#
+# Test that commands can be cleared without error.
+#
+
+gdb_test "commands\nprint 232323\nend" ">end" "set some breakpoint commands"
+gdb_test "commands\nend" ">end" "clear breakpoint commands"
+# We verify that the commands were cleared by ensuring that the last
+# breakpoint's location ends the output -- if there were commands,
+# they would have been printed after the location.
+gdb_test "info break" "$srcfile:$line" "verify that they were cleared"