Fix arithmetic exception due to menu->pagelen being negative.

Resizing the terminal window down to two lines when in an empty
mailbox causes mutt to crash due to division by zero since menu->max
equals 0 and menu->pagelen < 0 in status.c:205.

Fixing the problem at this specific line felt wrong since I did notice
menu->pagelen being negative. The pagelen is inherited from the rows
calculation in mutt_reflow_windows. Since the number of lines can
potentially be smaller than the accumulated number of rows acquired by
the status, help and message window, make sure the calculation does
not turn negative.

1 files changed, 2 insertions, 2 deletions

diff --git a/curs_lib.c b/curs_lib.c
index ed0d10c3..8b21c43f 100644
--- a/curs_lib.c
+++ b/curs_lib.c
@@ -531,8 +531,8 @@ void mutt_reflow_windows (void)
   MuttMessageWindow->row_offset = LINES - 1;
 
   memcpy (MuttIndexWindow, MuttStatusWindow, sizeof (mutt_window_t));
-  MuttIndexWindow->rows = LINES - MuttStatusWindow->rows - MuttHelpWindow->rows -
-                          MuttMessageWindow->rows;
+  MuttIndexWindow->rows = MAX(LINES - MuttStatusWindow->rows -
+			      MuttHelpWindow->rows - MuttMessageWindow->rows, 0);
   MuttIndexWindow->row_offset = option (OPTSTATUSONTOP) ? MuttStatusWindow->rows :
                                                           MuttHelpWindow->rows;