patch 8.1.0042: if omni completion opens a window Insert mode is stopped

Problem:    If omni completion opens a window Insert mode is stopped.
            (Hirohito Higashi)
Solution:   Only set stop_insert_mode in a prompt buffer window.

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    42,
 /**/
     41,
 /**/