patch 8.2.1923: Vim9: "filter" command modifier doesn't work

Problem:    Vim9: "filter" command modifier doesn't work.
Solution:   Check for space on char before argument. (closes #7216,
            closes #7222)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index b8ee85c..48da263 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -2763,7 +2763,7 @@
 			    }
 #ifdef FEAT_EVAL
 			    // Avoid that "filter(arg)" is recognized.
-			    if (in_vim9script() && !VIM_ISWHITE(*p))
+			    if (in_vim9script() && !VIM_ISWHITE(p[-1]))
 				break;
 #endif
 			    if (skip_only)
diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 710cd2f..61c47b8 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -312,6 +312,18 @@
   assert_equal([#{x: 3, y: 4}], tags)
 enddef
 
+def Test_filter_is_recognized()
+  var lines =<< trim END
+    final expected = "\nType Name Content\n  c  \"c   piyo"
+    @a = 'hoge'
+    @b = 'fuga'
+    @c = 'piyo'
+
+    assert_equal(execute('filter /piyo/ registers abc'), expected)
+  END
+  CheckDefAndScriptSuccess(lines)
+enddef
+
 def Test_eval_command()
   var from = 3
   var to = 5
diff --git a/src/version.c b/src/version.c
index 4e1d570..52d8683 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1923,
+/**/
     1922,
 /**/
     1921,