Preserve underscores between digits in map constant to filename conversion

[Rangi42]

Event::warp_map_name converts the map constant to a label, e.g. UNION_CAVE_1F to UnionCave1F. However, it doesn't appropriately handle a case that doesn't come up in pokecrystal, when the constant has an underscore between digits. LUSTER_APARTMENT_1_1F should convert to LusterApartment1_1F, not LusterApartment11F.

Here's a Python implementation for testing:

def constant2label(constant):
    label = ''
    downcase = False
    for c in constant:
        if downcase:
            c = c.lower()
        if c == '_':
            downcase = False
        else:
            label += c
            downcase = not c.isdigit()
    return label

[Rangi42]

This gives better results:

def constant2label(constant):
	label = ''
	wasletter = False
	wasdigit = False
	maybeunderscore = False
	for c in constant:
		if c != '_':
			if maybeunderscore and c.isdigit():
				label += '_'
			if wasletter:
				c = c.lower()
			label += c
			maybeunderscore = False
		elif wasdigit:
			maybeunderscore = True
		wasletter = c.isalpha()
		wasdigit = c.isdigit()
	return label