vim-patch:9.0.0259: crash with mouse click when not initialized (#21282)

Problem:    Crash with mouse click when not initialized.
Solution:   Check TabPageIdxs[] is not NULL.

80525751c5

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/mouse.c

@@ -467,6 +467,7 @@ bool do_mouse(oparg_T *oap, int c, int dir, long count, bool fixindent)
 
   start_visual.lnum = 0;
 
+  if (tab_page_click_defs != NULL) {  // only when initialized
     // Check for clicking in the tab page line.
     if (mouse_grid <= 1 && mouse_row == 0 && firstwin->w_winrow > 0) {
       if (is_drag) {
@@ -528,6 +529,7 @@ bool do_mouse(oparg_T *oap, int c, int dir, long count, bool fixindent)
       move_tab_to_mouse();
       return false;
     }
+  }
 
   // When 'mousemodel' is "popup" or "popup_setpos", translate mouse events:
   // right button up   -> pop-up menu

src/nvim/testdir/test_tabline.vim

@@ -147,4 +147,18 @@ func Test_tabline_20_format_items_no_overrun()
   set showtabline& tabline&
 endfunc
 
+func Test_mouse_click_in_tab()
+  " This used to crash because TabPageIdxs[] was not initialized
+  let lines =<< trim END
+      tabnew
+      set mouse=a
+      exe "norm \<LeftMouse>"
+  END
+  call writefile(lines, 'Xclickscript')
+  call RunVim([], [], "-e -s -S Xclickscript -c qa")
+
+  call delete('Xclickscript')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab