patch 8.2.3439: deleted lines go to wrong yank register

Problem:    Deleted lines go to wrong yank register.
Solution:   Reset y_append when not calling get_yank_register(). (Christian
            Brabandt, closes #8872)
diff --git a/src/ops.c b/src/ops.c
index fa6a4c4..dedeebf 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -695,6 +695,8 @@
 	    if (op_yank(oap, TRUE, FALSE) == OK)   // yank without message
 		did_yank = TRUE;
 	}
+	else
+	    reset_y_append(); // not appending to unnamed register
 
 	/*
 	 * Put deleted text into register 1 and shift number registers if the