patch 8.2.4821: crash when imported autoload script was deleted

Problem:    Crash when imported autoload script was deleted.
Solution:   Initialize local variable. (closes #10274)  Give a more meaningful
            error message.

src/eval.c

@@ -6159,7 +6159,7 @@ handle_subscript(
 	    char_u	*exp_name;
 	    int		cc;
 	    int		idx;
-	    ufunc_T	*ufunc;
+	    ufunc_T	*ufunc = NULL;
 	    type_T	*type;
 
 	    // Found script from "import {name} as name", script item name must

src/testdir/test_vim9_import.vim

@@ -1137,6 +1137,25 @@ def Test_autoload_import_relative_autoload_dir()
   delete('autoload', 'rf')
 enddef
 
+def Test_autoload_import_deleted()
+  var lines =<< trim END
+      vim9script
+      export const FOO = 1
+  END
+  writefile(lines, 'Xa.vim')
+
+  lines =<< trim END
+      vim9script
+      import autoload './Xa.vim'
+
+      delete('Xa.vim')
+      var x = Xa.FOO
+  END
+  v9.CheckScriptFailure(lines, 'E484:')
+
+  delete('Xdir', 'rf')
+enddef
+
 func Test_import_in_diffexpr()
   CheckExecutable diff
 

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4821,
 /**/
     4820,
 /**/

src/vim9script.c

@@ -713,7 +713,10 @@ find_exported(
     if (script->sn_import_autoload && script->sn_state == SN_STATE_NOT_LOADED)
     {
 	if (do_source(script->sn_name, FALSE, DOSO_NONE, NULL) == FAIL)
+	{
+	    semsg(_(e_cant_open_file_str), script->sn_name);
 	    return -1;
+	}
     }
 
     // Find name in "script".