patch 8.2.1873: Vim9: missing white space when using <f-args>

Problem:    Vim9: missing white space when using <f-args>.
Solution:   Add spaces. (Christian J. Robinson)
diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 599c287..ad3454d 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -375,6 +375,24 @@
   bwipe!
 enddef
 
+def Test_f_args()
+  var lines =<< trim END
+    vim9script
+
+    func SaveCmdArgs(...)
+      let g:args = a:000
+    endfunc
+
+    command -nargs=* TestFArgs call SaveCmdArgs(<f-args>)
+
+    TestFArgs
+    assert_equal([], g:args)
+
+    TestFArgs one two three
+    assert_equal(['one', 'two', 'three'], g:args)
+  END
+  CheckScriptSuccess(lines)
+enddef
 
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/usercmd.c b/src/usercmd.c
index de49d41..261a629 100644
--- a/src/usercmd.c
+++ b/src/usercmd.c
@@ -1153,7 +1153,7 @@
 	    p = skipwhite(p);
 	    if (*p == NUL)
 		break;
-	    len += 3; // ","
+	    len += 4; // ", "
 	}
 	else
 	{
@@ -1199,6 +1199,7 @@
 		break;
 	    *q++ = '"';
 	    *q++ = ',';
+	    *q++ = ' ';
 	    *q++ = '"';
 	}
 	else
diff --git a/src/version.c b/src/version.c
index dd34356..08da992 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1873,
+/**/
     1872,
 /**/
     1871,