patch 8.2.4594: need to write script to a file to be able to source them

Problem:    Need to write script to a file to be able to source them.
Solution:   Make ":source" use lines from the current buffer. (Yegappan
            Lakshmanan et al., closes #9967)
diff --git a/src/digraph.c b/src/digraph.c
index bbab958..9fdd0b3 100644
--- a/src/digraph.c
+++ b/src/digraph.c
@@ -2507,7 +2507,7 @@
     int		i;
     char_u	*save_cpo = p_cpo;
 
-    if (!getline_equal(eap->getline, eap->cookie, getsourceline))
+    if (!sourcing_a_script(eap))
     {
 	emsg(_(e_using_loadkeymap_not_in_sourced_file));
 	return;