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)

src/testdir/test_vim9_cmd.vim

@@ -375,6 +375,24 @@ def Test_command_star_range()
   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

src/usercmd.c

@@ -1153,7 +1153,7 @@ uc_split_args(char_u *arg, size_t *lenp)
 	    p = skipwhite(p);
 	    if (*p == NUL)
 		break;
-	    len += 3; // ","
+	    len += 4; // ", "
 	}
 	else
 	{
@@ -1199,6 +1199,7 @@ uc_split_args(char_u *arg, size_t *lenp)
 		break;
 	    *q++ = '"';
 	    *q++ = ',';
+	    *q++ = ' ';
 	    *q++ = '"';
 	}
 	else

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1873,
 /**/
     1872,
 /**/