vi: deal with invalid movements in shift commands

Since commit 25d259264 (vi: make buffer handling more vi-like)
find_range() can return early when an invalid movement is
specified.

The call to find_range() in the code that handles shift commands
('<' and '>') doesn't check for this condition.  Previously this
only resulted in the current line being shifted but it can now
result in a segfault.

Check for an invalid movement and notify the user without taking
any further action.

function                                             old     new   delta
do_cmd                                              4890    4898      +8
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/0 up/down: 8/0)                 Total: 8 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/editors/vi.c b/editors/vi.c
index 4fa67a110..04d584fec 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -7,7 +7,6 @@
  */
 //
 //Things To Do:
-//      EXINIT
 //      $HOME/.exrc  and  ./.exrc
 //      add magic to search     /foo.*bar
 //      add :help command
@@ -3574,7 +3573,10 @@ static void do_cmd(int c)
         case '>':                       // >- Right shift something
                 cnt = count_lines(text, dot);   // remember what line we are on
                 c1 = get_motion_char(); // get the type of thing to operate on
-                find_range(&p, &q, c1);
+                if (find_range(&p, &q, c1) == -1) {
+                        indicate_error();
+                        goto dc6;
+                }
                 yank_delete(p, q, WHOLE, YANKONLY, NO_UNDO);    // save copy before change
                 p = begin_line(p);
                 q = end_line(q);