Stop special input functions "and" & "or" from tearing up multi-char binding

The tentative binding for the upcoming "history-pager-delete" is

    bind -k sdc history-pager-delete or backward-delete-char

When Shift+Delete is pressed while the history pager is active,
"history-pager-delete" succeeds. In this case, the "or" needs to kick the
"backward-delete-char" out of the input queue.
After doing so, it continues reading, but interprets the input as
single-char binding. This breaks when the next key emits a multi-char sequence,
like the arrow keys.

Fix this by reading a full sequence, which means we need to run "read_char()"
instead of "read_ch()" (confusing, right?).

I'm still working on writing a test. Somehow this only reproduces in the
history pager where Shift+Delete followed by down arrow emits "[B" (since
we swallowed the leading escape char).  Confusingly, it doesn't do that in
the commandline or the completion search field.

src/input.cpp

@@ -764,7 +764,7 @@ char_event_t inputter_t::read_char(const command_handler_t &command_handler) {
                         evt = this->readch();
                     } while (evt.is_readline());
                     this->push_front(evt);
-                    return readch();
+                    continue;
                 }
                 default: {
                     return evt;