patch 8.2.1901: variable completion does not work in command line window

Problem:    Variable completion does not work in command line window.
Solution:   Use the "prevwin". (closes #7198)
diff --git a/src/version.c b/src/version.c
index 7aa2e10..5a36f06 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1901,
+/**/
     1900,
 /**/
     1899,