Move kernel size check into getlist()

[radarhere]

Within _prepare_lut_table(), _point() and _transform(), a size is passed to getlist()

Pillow/src/_imaging.c

Line 878 in 0253ef0

table_data = getlist(table, &table_size, wrong_size, TYPE_FLOAT32);

which then checks it and raises a ValueError if it is incorrect.

Pillow/src/_imaging.c

Lines 447 to 450 in 0253ef0

	if (length && wrong_length && n != *length) {
	PyErr_SetString(PyExc_ValueError, wrong_length);
	return NULL;
	}

However, _filter() asks getlist() for the length and then checks it afterwards.

Pillow/src/_imaging.c

Line 1170 in 0253ef0

kerneldata = getlist(kernel, &kernelsize, NULL, TYPE_FLOAT32);

Pillow/src/_imaging.c

Lines 496 to 498 in 0253ef0

	if (length) {
	*length = n;
	}

Pillow/src/_imaging.c

Lines 1174 to 1177 in 0253ef0

	if (kernelsize != (Py_ssize_t)xsize * (Py_ssize_t)ysize) {
	free(kerneldata);
	return ImagingError_ValueError("bad kernel size");
	}

It would be simpler to use the same strategy for all scenarios.