Fix #1736: on GNU/Linux, a hotkey can trigger multiple commands

SDL_TEXTINPUT events aren't generated on Windows when Alt is held down.
Let's ensure that the behavior is the same on all platforms.

src/events.cpp

@@ -487,6 +487,15 @@ void pump()
 		events.erase(first_draw_event + 1, events.end());
 	}
 
+	if(SDL_GetModState() & KMOD_ALT) {
+		// Remove text input events, to match the behavior on Windows
+		// See https://github.com/wesnoth/wesnoth/issues/1736
+		events.erase(
+			std::remove_if(events.begin(), events.end(), [](const SDL_Event& e) { return e.type == SDL_TEXTINPUT; }),
+			events.end()
+		);
+	}
+
 	ev_end = events.end();
 
 	for(ev_it = events.begin(); ev_it != ev_end; ++ev_it) {