Language server erroring when indexing empty parentheses #570

-- Same thing with `:` instead of `.`
local t = ().

script\parser\guide.lua:975: attempt to index a nil value (local 'source')
stack traceback:
	script\core\noder.lua:190: in upvalue 'checkMode'
	script\core\noder.lua:326: in function <script\core\noder.lua:282>
	(...tail calls...)
	script\core\searcher.lua:689: in upvalue 'prepareSearch'
	script\core\searcher.lua:783: in function 'core.searcher.searchRefs'
	script\core\searcher.lua:878: in function 'core.searcher.requestReference'
	(...tail calls...)
	script\core\highlight.lua:10: in upvalue 'eachRef'
	script\core\highlight.lua:33: in upvalue 'find'
	script\core\highlight.lua:251: in function 'core.highlight'
	script\provider\provider.lua:381: in function <script\provider\provider.lua:374>
	[C]: in function 'xpcall'
	script\proto\proto.lua:143: in function <script\proto\proto.lua:122>