patch 8.1.0022: repeating put from expression register fails

Problem:    Repeating put from expression register fails.
Solution:   Re-evaluate the expression register. (Andy Massimino,
            closes #2945)
diff --git a/src/getchar.c b/src/getchar.c
index ddb23dd..ff03905 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -844,6 +844,14 @@
 	if (c >= '1' && c < '9')
 	    ++c;
 	add_char_buff(&readbuf2, c);
+
+	/* the expression register should be re-evaluated */
+	if (c == '=')
+	{
+	    add_char_buff(&readbuf2, CAR);
+	    cmd_silent = TRUE;
+	}
+
 	c = read_redo(FALSE, old_redo);
     }