patch 8.2.1934: Vim9: command modifiers in :def function not tested

Problem:    Vim9: command modifiers in :def function not tested.
Solution:   Add tests.  Fix using modifier before filter command.
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 48da263..d2cc05f 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -1782,14 +1782,27 @@
  */
     cmd = ea.cmd;
 #ifdef FEAT_EVAL
-    // In Vim9 script a colon is required before the range.
-    may_have_range = !vim9script || starts_with_colon;
+    // In Vim9 script a colon is required before the range.  This may also be
+    // after command modifiers.
+    if (vim9script)
+    {
+	may_have_range = FALSE;
+	for (p = ea.cmd; p >= *cmdlinep; --p)
+	{
+	    if (*p == ':')
+		may_have_range = TRUE;
+	    if (p < ea.cmd && !VIM_ISWHITE(*p))
+		break;
+	}
+    }
+    else
+	may_have_range = TRUE;
     if (may_have_range)
 #endif
 	ea.cmd = skip_range(ea.cmd, TRUE, NULL);
 
 #ifdef FEAT_EVAL
-    if (vim9script && !starts_with_colon)
+    if (vim9script && !may_have_range)
     {
 	if (ea.cmd == cmd + 1 && *cmd == '$')
 	    // should be "$VAR = val"