patch 8.2.1762: when a timer uses :stopinsert completion isn't stopped

Problem:    When a timer uses :stopinsert Insert mode completion isn't
            stopped. (Stanley Chan)
Solution:   Call ins_compl_prep(ESC).
diff --git a/src/edit.c b/src/edit.c
index 642ff95..e3e4624 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -587,8 +587,11 @@
 		if (stop_insert_mode)
 		{
 		    // Insert mode ended, possibly from a callback.
+		    if (c != K_IGNORE && c != K_NOP)
+			vungetc(c);
 		    count = 0;
 		    nomove = TRUE;
+		    ins_compl_prep(ESC);
 		    goto doESCkey;
 		}
 	    } while (c == K_IGNORE || c == K_NOP);