Disable SDL text input events before actually focusing a text input element. Patch by echotangoecho, refs #3870.

Thus don't add a "t" to the chat input after opening it with the hotkey
on unix.
The bug still occurs on Windows due to an SDL bug reported upstream by
echotangoecho.

This was SVN commit r18990.

source/ps/GameSetup/GameSetup.cpp

@@ -684,6 +684,9 @@ static void InitSDL()
 	}
 	atexit(SDL_Quit);
 
+	// Text input is active by default, disable it until it is actually needed.
+	SDL_StopTextInput();
+
 #if OS_MACOSX
 	// Some Mac mice only have one button, so they can't right-click
 	// but SDL2 can emulate that with Ctrl+Click