patch 8.2.1455: Vim9: crash when using typecast before constant

Problem:    Vim9: crash when using typecast before constant.
Solution:   Generate constant before checking type.  Add tets.

Author: brammool

src/testdir/test_vim9_expr.vim

@@ -1324,6 +1324,12 @@ let $TESTVAR = 'testvar'
 def Test_expr7t()
   let ls: list<string> = ['a', <string>g:string_empty]
   let ln: list<number> = [<number>g:anint, <number>g:alsoint]
+  let nr = <number>234
+  assert_equal(234, nr)
+
+  call CheckDefFailure(["let x = <nr>123"], 'E1010:')
+  call CheckDefFailure(["let x = <number >123"], 'E1068:')
+  call CheckDefFailure(["let x = <number 123"], 'E1104:')
 enddef
 
 " test low level expression

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1455,
 /**/
     1454,
 /**/

src/vim9compile.c

@@ -3501,11 +3501,12 @@ compile_expr7t(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
     if (want_type != NULL)
     {
 	garray_T    *stack = &cctx->ctx_type_stack;
-	type_T	    *actual = ((type_T **)stack->ga_data)[stack->ga_len - 1];
+	type_T	    *actual;
 
+	generate_ppconst(cctx, ppconst);
+	actual = ((type_T **)stack->ga_data)[stack->ga_len - 1];
 	if (check_type(want_type, actual, FALSE) == FAIL)
 	{
-	    generate_ppconst(cctx, ppconst);
 	    if (need_type(actual, want_type, -1, cctx, FALSE) == FAIL)
 		return FAIL;
 	}
@@ -5016,6 +5017,7 @@ compile_assignment(char_u *arg, exarg_T *eap, cmdidx_T cmdidx, cctx_T *cctx)
 		goto theend;
 	    if (*skipwhite(p) != ']')
 	    {
+		// this should not happen
 		emsg(_(e_missbrac));
 		goto theend;
 	    }