patch 9.0.0211: invalid memory access when compiling :lockvar

Problem:    Invalid memory access when compiling :lockvar.
Solution:   Don't read past the end of the line.

src/testdir/test_vim9_cmd.vim

@@ -1737,6 +1737,15 @@ def Test_lockvar()
       UnLockIt()
   END
   v9.CheckScriptFailure(lines, 'E46', 1)
+
+  lines =<< trim END
+      def _()
+        s:0([], s:0)
+        lockv
+      enddef
+      defcomp
+  END
+  v9.CheckScriptFailure(lines, 'E179', 2)
 enddef
 
 def Test_substitute_expr()

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    211,
 /**/
     210,
 /**/

src/vim9cmds.c

@@ -188,10 +188,17 @@ compile_lock_unlock(
     size_t	len;
     char_u	*buf;
     isntype_T	isn = ISN_EXEC;
+    char	*cmd = eap->cmdidx == CMD_lockvar ? "lockvar" : "unlockvar";
 
     if (cctx->ctx_skip == SKIP_YES)
 	return OK;
 
+    if (*p == NUL)
+    {
+	semsg(_(e_argument_required_for_str), cmd);
+	return FAIL;
+    }
+
     // Cannot use :lockvar and :unlockvar on local variables.
     if (p[1] != ':')
     {
@@ -223,8 +230,6 @@ compile_lock_unlock(
 	ret = FAIL;
     else
     {
-	char *cmd = eap->cmdidx == CMD_lockvar ? "lockvar" : "unlockvar";
-
 	if (deep < 0)
 	    vim_snprintf((char *)buf, len, "%s! %s", cmd, p);
 	else