only add circuitpython_splash to display if it's not in another group

[FoamyGuy]

resolves #7824

Tested successfully on Monster M4sk

Not sure if we need to guard more cautiously against circuitpython_splash being null or not having in_group. This code assumes it will exist and have that property to check. It does seem safe after testing on Monster M4sk but I don't know if there are other scenarios that could be problematic.

[gamblor21]

This code looks fine, but I noticed a few lines later it checks if root_group is NULL and if so assigns it to circuitpython_splash with no checks and not using the function. Not sure how that may affect anything. But your check on its own looks good.

[Neradoc]

Are you talking about when calling display.show(None) ? It uses common_hal_displayio_display_show which does a few checks, including if the group is already in a group, and returns False when those checks fail. That return is checked and an exception is raised in the shared-bindings part:

circuitpython/shared-bindings/displayio/Display.c

Lines 261 to 264 in 4e7bbf7

	bool ok = common_hal_displayio_display_show(self, group);
	if (!ok) {
	mp_raise_ValueError(translate("Group already used"));
	}

Maybe it could use common_hal_displayio_display_set_root_group instead. (show() is deprecated anyway).

[FoamyGuy]

The latest commit adds the same check as the original commit but to a different section of code inside reset_display() which had caused trouble raised by #7472

[tannewt]

Looks good to me! Thank you!