patch 8.2.3651: Vim9: no error for :lock or :unlock with unknown variable

Problem:    Vim9: no error for :lock or :unlock with unknown variable.
Solution:   Give an error. (closes #9188)

src/errors.h

@@ -686,3 +686,5 @@ EXTERN char e_bad_color_string_str[]
 	INIT(= N_("E1244: Bad color string: %s"));
 EXTERN char e_cannot_expand_sfile_in_vim9_function[]
 	INIT(= N_("E1245: Cannot expand <sfile> in a Vim9 function"));
+EXTERN char e_cannot_find_variable_to_unlock_str[]
+	INIT(= N_("E1246: Cannot find variable to (un)lock: %s"));

src/evalvars.c

@@ -1827,7 +1827,12 @@ do_lock_var(
 	    // Normal name or expanded name.
 	    di = find_var(lp->ll_name, NULL, TRUE);
 	    if (di == NULL)
+	    {
+		if (in_vim9script())
+		    semsg(_(e_cannot_find_variable_to_unlock_str),
+								  lp->ll_name);
 		ret = FAIL;
+	    }
 	    else if ((di->di_flags & DI_FLAGS_FIX)
 			    && di->di_tv.v_type != VAR_DICT
 			    && di->di_tv.v_type != VAR_LIST)

src/testdir/test_vim9_cmd.vim

@@ -1370,6 +1370,23 @@ def Test_lockvar()
       unlockvar theList
   END
   CheckDefFailure(lines, 'E1178', 2)
+
+  lines =<< trim END
+      vim9script
+      var name = 'john'
+      lockvar nameX
+  END
+  CheckScriptFailure(lines, 'E1246', 3)
+
+  lines =<< trim END
+      vim9script
+      var name = 'john'
+      def LockIt()
+        lockvar nameX
+      enddef
+      LockIt()
+  END
+  CheckScriptFailure(lines, 'E1246', 1)
 enddef
 
 def Test_substitute_expr()

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3651,
 /**/
     3650,
 /**/