fix(startup): avoid crash with completion from -l script (#32160)

Related #27764

src/nvim/drawscreen.c

@@ -177,14 +177,11 @@ bool default_grid_alloc(void)
   resizing = true;
 
   // Allocation of the screen buffers is done only when the size changes and
-  // when Rows and Columns have been set and we have started doing full
-  // screen stuff.
+  // when Rows and Columns have been set.
   if ((default_grid.chars != NULL
        && Rows == default_grid.rows
        && Columns == default_grid.cols)
-      || Rows == 0
-      || Columns == 0
-      || (!full_screen && default_grid.chars == NULL)) {
+      || Rows == 0 || Columns == 0) {
     resizing = false;
     return false;
   }

src/nvim/main.c

@@ -360,7 +360,7 @@ int main(int argc, char **argv)
 
   setbuf(stdout, NULL);  // NOLINT(bugprone-unsafe-functions)
 
-  full_screen = !silent_mode || exmode_active;
+  full_screen = !silent_mode;
 
   // Set the default values for the options that use Rows and Columns.
   win_init_size();

test/functional/core/main_spec.lua

@@ -67,12 +67,22 @@ describe('command-line option', function()
       eq(#'100500\n', attrs.size)
     end)
 
-    it('does not crash when run completion in Ex mode', function()
+    it('does not crash when running completion in Ex mode', function()
       local p =
         n.spawn_wait('--clean', '-e', '-s', '--cmd', 'exe "norm! i\\<C-X>\\<C-V>"', '--cmd', 'qa!')
       eq(0, p.status)
     end)
 
+    it('does not crash when running completion from -l script', function()
+      local lua_fname = 'Xinscompl.lua'
+      write_file(lua_fname, [=[vim.cmd([[exe "norm! i\<C-X>\<C-V>"]])]=])
+      finally(function()
+        os.remove(lua_fname)
+      end)
+      local p = n.spawn_wait('--clean', '-l', lua_fname)
+      eq(0, p.status)
+    end)
+
     it('does not crash after reading from stdin in non-headless mode', function()
       skip(is_os('win'))
       local screen = Screen.new(40, 8)