When using `SDL_ConvertEventToRenderCoordinates` with
`SDL_EVENT_FINGER_MOTION` events it converts `x` and `y` coordinates but
does not convert the the `dx` and the `dy` unlike `xrel` and `yrel` of
mouse motion events. This is means that these are rather useless after
conversion. This change unifies this behavior between touch and mouse
motion events.
Creating `argv` for zenity means we don't have to pass the building
blocks between threads which allows us to avoid deep copying some nested
structures. It also allows us to fail earlier in case of problems with
building the argument vector.
SDL properties passed to the `SDL_Zenity_ShowFileDialogWithProperties`
may be destroyed/modified immediately upon the function return.
Therefore, we must copy all the strings and structures passed via
pointers; otherwise, the `SDL_ZenityFileDialog` thread attempting to
read them will cause data race.
The double quotes were passed literally to the zenity arguments which
resulted in the message box displaying literal `""` when no text was
given. The empty string is more logical in this case, e.g., the empty
title results in the message box having lesser height.
When no extra buttons are passed to zenity with `--question --switch`
arguments it fails to show anything, however, SDL3 still reports
success. To handle this case, we pass an additional "OK" button.
Marcin Serwin