Fix syncing observations with no identifications

If no identifications were present on the observation, there will not be
any keywords to be set. If there are no keywords, don't try to examine
the kw object to set keywords on the photo...

lr-inaturalist-publish.lrdevplugin/SyncObservations.lua

@@ -241,6 +241,10 @@ local function kwIsEquivalent(kw, hierarchy, rootId)
 end
 
 local function syncKeywords(photo, kw, settings, keywordCache)
+	if not kw then
+		return
+	end
+
 	local unwanted = {}
 	local needsAddition = true
 	if settings.syncKeywords and kw then