patch 9.0.1623: the program to filetype translation is not exported

Problem:    The program to filetype translation is not exported.
Solution:   Export Exe2filetype().
diff --git a/src/version.c b/src/version.c
index ddc30c2..8d38d36 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1623,
+/**/
     1622,
 /**/
     1621,