Do not auto apply the fallback regex when in regex prompts

Fixes #1653

src/input_handler.cc

@@ -968,7 +968,8 @@ private:
     {
         display();
         m_line_changed = false;
-        m_callback(m_line_editor.line(), PromptEvent::Change, context());
+        m_callback((m_flags & PromptFlags::InactiveInitString) ? StringView{} : m_line_editor.line(),
+                   PromptEvent::Change, context());
 
         if (not (context().flags() & Context::Flags::Transient))
             m_idle_timer.set_next_date(Clock::now() + get_idle_timeout(context()));

src/normal.cc

@@ -718,6 +718,7 @@ void regex_prompt(Context& context, String prompt, String default_regex, T func)
                 if (event == PromptEvent::Validate)
                     context.push_jump();
 
+                if (not str.empty() or event == PromptEvent::Validate)
                     func(str.empty() ? Regex{default_regex} : Regex{str}, event, context);
             }
             catch (regex_error& err)