patch 8.2.3649: Vim9: error for variable declared in while loop

Problem:    Vim9: error for variable declared in while loop.
Solution:   Do not keep the first variable. (closes #9191)

src/ex_eval.c

@@ -1201,9 +1201,10 @@ ex_while(exarg_T *eap)
 								& CSF_FUNC_DEF;
 
 		// Any variables defined in the previous round are no longer
-		// visible.  Keep the first one, it is the loop variable that
-		// we reuse every time around.
-		for (i = cstack->cs_script_var_len[cstack->cs_idx] + 1;
+		// visible.  Keep the first one for ":for", it is the loop
+		// variable that we reuse every time around.
+		for (i = cstack->cs_script_var_len[cstack->cs_idx]
+					  + (eap->cmdidx == CMD_while ? 0 : 1);
 					       i < si->sn_var_vals.ga_len; ++i)
 		{
 		    svar_T	*sv = ((svar_T *)si->sn_var_vals.ga_data) + i;

src/testdir/test_vim9_script.vim

@@ -3083,6 +3083,21 @@ def Test_while_loop()
   endwhile
 enddef
 
+def Test_while_loop_in_script()
+  var lines =<< trim END
+      vim9script
+      var result = ''
+      var cnt = 0
+      while cnt < 3
+        var s = 'v' .. cnt
+        result ..= s
+        cnt += 1
+      endwhile
+      assert_equal('v0v1v2', result)
+  END
+  CheckScriptSuccess(lines)
+enddef
+
 def Test_while_loop_fails()
   CheckDefFailure(['while xxx'], 'E1001:')
   CheckDefFailure(['endwhile'], 'E588:')

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3649,
 /**/
     3648,
 /**/