Fix #7: Pressing return crashes Input.

Add arguments to call of keyboard.pressed() in input.lua.
Add sanity check to keyboard.pressed().

input.lua

@@ -63,7 +63,7 @@ return function(w)
 	-- info
 	elseif keyboard.key == 'return' then
 		keyboard.clearFocus()
-		keyboard.pressed()
+		keyboard.pressed('', -1)
 	elseif keyboard.code >= 32 and keyboard.code < 127 then
 		local left = w.info.text:sub(1,w.info.cursor)
 		local right =  w.info.text:sub(w.info.cursor+1)

keyboard.lua

@@ -34,7 +34,11 @@ local cycle = {
 	next = {key = 'tab'},
 }
 
-local function pressed(...) key, code = ... end
+local function pressed(...)
+	key, code = ...
+	assert(type(key) == 'string', 'Invalid argument `key`. Expected string, got ' .. type(key))
+	assert(type(code) == 'number', 'Invalid argument `code`. Expected number, got ' .. type(code))
+end
 local function setFocus(id) focus = id end
 local function disable()    focus = NO_WIDGET end
 local function clearFocus() focus = nil end