lualoader: improve drawer error handling

At least one user has landed in a scenario where logo files appear to be
misnamed, and we failed to find them. Our fallback for missing logodefs is
orb/orbbw, based on the color status. In a scenario where we can't locate
the logos, though, this is not ideal. Add in one more layer of fallback
to properly just don't draw any logo if the fan has been jam packed with
foreign material.

PR:		246046
MFC after:	3 days

stand/lua/drawer.lua

@@ -258,6 +258,11 @@ local function drawlogo()
 		else
 			logodef = getLogodef(drawer.default_bw_logodef)
 		end
+
+		-- Something has gone terribly wrong.
+		if logodef == nil then
+			logodef = getLogodef(drawer.default_fallback_logodef)
+		end
 	end
 
 	if logodef ~= nil and logodef.graphic == none then
@@ -355,6 +360,9 @@ shift = default_shift
 drawer.default_brand = 'fbsd'
 drawer.default_color_logodef = 'orb'
 drawer.default_bw_logodef = 'orbbw'
+-- For when things go terribly wrong; this def should be present here in the
+-- drawer module in case it's a filesystem issue.
+drawer.default_fallback_logodef = 'none'
 
 function drawer.addBrand(name, def)
 	branddefs[name] = def