Default saved variables with 'or {}' instead of overwriting

Seed the SavedVariables globals only when absent (X = X or {}) rather
than unconditionally assigning {}. Behaviorally identical under the
current load order -- a returning character's data is restored over these
between file load and ADDON_LOADED -- but expresses intent as a default
and won't clobber data if that timing ever changed.

pfUI.lua

@@ -86,14 +86,13 @@ do
   end
 end
 
--- initialize saved variables
-pfUI_playerDB = {}
-pfUI_config = {}
-pfUI_init = {}
-pfUI_profiles = {}
-pfUI_addon_profiles = {}
-pfUI_cache = {}
-pfUI_throttle = {}
+pfUI_playerDB = pfUI_playerDB or {}
+pfUI_config = pfUI_config or {}
+pfUI_init = pfUI_init or {}
+pfUI_profiles = pfUI_profiles or {}
+pfUI_addon_profiles = pfUI_addon_profiles or {}
+pfUI_cache = pfUI_cache or {}
+pfUI_throttle = pfUI_throttle or {}
 
 -- localization
 pfUI_locale = {}