luci-compat: CBI skip fields that do not satisfy depends

If depends is not satisfied, the fvalue will be nil.

Signed-off-by: Liangbin Lian <jjm2473@gmail.com>

Author: jjm2473

modules/luci-compat/luasrc/cbi.lua

@@ -1443,7 +1443,7 @@ function AbstractValue.parse(self, section, novld)
 				--luci.util.append(self.map.events, self.events)
 			end
 		end
-	else							-- Unset the UCI or error
+	elseif fvalue ~= nil then			-- Unset the UCI or error
 		if self.rmempty or self.optional then
 			if not self.alias or
 			   not self.section.aliased or