Fixed psionic gem wielding when the gem has no material level

git-svn-id: http://svn.net-core.org/repos/t-engine4@2546 51575b47-30f0-44d4-a5cc-537603b46e54

game/modules/tome/data/talents/psionic/psionic.lua

@@ -121,7 +121,7 @@ function getGemLevel(self)
 	if self:getInven("PSIONIC_FOCUS") then
 		local tk_item = self:getInven("PSIONIC_FOCUS")[1]
 		if tk_item and (tk_item.type == "gem") then
-			gem_level = tk_item.material_level
+			gem_level = tk_item.material_level or 0
 		end
 	end
 	return gem_level