MP jpegdec: fix width/height functions by opening file/buffer earlier

[Skyler84]

References #894
Open file/buffer in open function rather than on demand.
Also adds a close function for the user.

[Gadgetoid]

Thank you!

I think we should probably copy the pattern from the PNG image parsing, since introducing a requirement on calling close now will no doubt break people's code in unexpected ways.

PNGDEC's bindings open the file, read out the dimensions, then close it until it's ready to be decoded:

pimoroni-pico/micropython/modules/pngdec/pngdec.cpp

Lines 292 to 321 in bff2453

	mp_obj_t _PNG_openFILE(mp_obj_t self_in, mp_obj_t filename) {
	_PNG_obj_t *self = MP_OBJ_TO_PTR2(self_in, _PNG_obj_t);
	// TODO Check for valid filename, and maybe that file exists?
	self->file = filename;
	pngdec_open_helper(self);
	self->width = self->png->getWidth();
	self->height = self->png->getHeight();
	self->png->close();
	return mp_const_true;
	}
	// open_RAM
	mp_obj_t _PNG_openRAM(mp_obj_t self_in, mp_obj_t buffer) {
	_PNG_obj_t *self = MP_OBJ_TO_PTR2(self_in, _PNG_obj_t);
	// TODO Check for valid buffer
	self->file = buffer;
	pngdec_open_helper(self);
	self->width = self->png->getWidth();
	self->height = self->png->getHeight();
	self->png->close();
	return mp_const_true;
	}

[Gadgetoid]

Sorry I totally missed that you'd updated the PR! Will look into what's making the CI unhappy.

Looks like it's self->decode_callback should just be JPEGDraw and the int result = -1 is needed at the top of _JPEG_decode

Otherwise, thank you!

[Skyler84]

I'd been silly and missed an int declaration was all. should build fine now