scripts/device: avoid crashing if the device.name is not set

This should never happen, but there are odd cases with broken
configuration where such a device may appear and the least we can do
is not crash, at least not when the device.name is only used for
debug messages. In state-profile and other places where the name
really matters, we actually have checks in place.

Fixes: #674

src/scripts/device/apply-profile.lua

@@ -23,7 +23,7 @@ AsyncEventHook {
       execute = function (event, transition)
         local device = event:get_subject ()
         local profile = event:get_data ("selected-profile")
-        local dev_name = device.properties ["device.name"]
+        local dev_name = device.properties ["device.name"] or ""
 
         if not profile then
           log:info (device, "No profile found to set on " .. dev_name)

src/scripts/device/find-best-profile.lua

@@ -28,7 +28,7 @@ SimpleEventHook {
     end
 
     local device = event:get_subject ()
-    local dev_name = device.properties["device.name"]
+    local dev_name = device.properties["device.name"] or ""
     local off_profile = nil
     local best_profile = nil
     local unk_profile = nil