Verify indexed pixels contained on palette (if palette is not at capacity)

[Brett208]

IndexedBmpWriter will extend the palette, which will ensure all pixels indices are contained on the palette. However, it should be possible to detect if a pixel index is out of range before the palette is extended.

A first draft of the function is:

void IndexedBmpWriter::VerifyPixelsContainedInPalette(uint16_t bitCount, std::size_t paletteEntryCount, const std::vector<uint8_t>& pixels)
{
	// Check if palette is full
	// Use explicit size_t type to avoid compiler warnings for signedness or size
	if (paletteEntryCount == std::size_t{1} << bitCount) {
		return;
	}

	if (bitCount == 1) {
		for (const auto& pixelGroup : pixels) {
			if (pixelGroup > 0) {
				throw (std::runtime_error("A pixel is outside the range of set palette indices."));
			}
		}
	}

	if (bitCount == 4) {
		return; //TODO: Support checking 2 bit images
	}

	for (std::size_t i = 0; i < pixels.size(); ++i) {
		if (pixels[i] >= paletteEntryCount) {
			throw std::runtime_error("Pixel " + std::to_string(i) + " is outside the range of set palette indices.");
		}
	}
}