patch 9.1.0015: i_CTRL-R- no longer works in replace mode

Problem:  i_CTRL-R- no longer works in replace mode
Solution: delete characters in replace mode before putting, add a test,
          add a bit warning into the documentation, that i_CTRL-R-P/O
          is not supported in Replace mode for now

fixes: #13792
closes: #13816

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/register.c b/src/register.c
index 1d0e46b..f381e30 100644
--- a/src/register.c
+++ b/src/register.c
@@ -828,9 +828,22 @@
 	    {
 		if (regname == '-')
 		{
+		    int dir = BACKWARD;
+		    if ((State & REPLACE_FLAG) != 0)
+		    {
+			pos_T curpos;
+			u_save_cursor();
+			del_bytes((long)STRLEN(y_current->y_array[0]), TRUE, FALSE);
+			curpos = curwin->w_cursor;
+			if (oneright() == FAIL)
+			    // hit end of line, need to put forward (after the current position)
+			    dir = FORWARD;
+			curwin->w_cursor = curpos;
+		    }
+
 		    AppendCharToRedobuff(Ctrl_R);
 		    AppendCharToRedobuff(regname);
-		    do_put(regname, NULL, BACKWARD, 1L, PUT_CURSEND);
+		    do_put(regname, NULL, dir, 1L, PUT_CURSEND);
 		}
 		else
 		    stuffescaped(y_current->y_array[i], literally);