nameplates: filter libunitscan by player/npc to dodge name collisions

GetUnitInfo() probed the players table first, so an NPC sharing a name
with a known player (e.g. Chromie) inherited the player's class, level,
and guild. Adds an isPlayer hint to GetUnitInfo and resolves each
plate's actual unit type from its cached GUID via UnitIsPlayer before
the lookup. The plate's cache.player gates further work.

libs/libunitscan.lua

@@ -10,10 +10,12 @@ setfenv(1, pfUI:GetEnvironment())
 -- on further expansions.
 --
 -- External functions:
---   GetUnitInfo(name, active)
+--   GetUnitInfo(name, active, isPlayer)
 --     Returns information of the given unitname. Returns nil if no match is found.
 --     When nothing is found and the active flag is set, the autoscanner will
 --     automatically pick it up and try to fill the missing entry by targetting the unit.
+--     Pass isPlayer=true/false to restrict the lookup to the players or mobs table
+--     (avoids name-collision false positives, e.g. a player and an NPC named Chromie).
 --
 --     class[String] - The class of the unit
 --     level[Number] - The level of the unit
@@ -44,11 +46,11 @@ local function RememberByUnit(unit, name, class)
   C_PlayerCache.RememberPlayer(guid, name, class, UnitRace(unit), UnitSex(unit))
 end
 
-function GetUnitInfo(name, active)
-  if units["players"][name] then
+function GetUnitInfo(name, active, isPlayer)
+  if isPlayer ~= false and units["players"][name] then
     local ret = units["players"][name]
     return ret.class, ret.level, ret.elite, true, ret.guild
-  elseif units["mobs"][name] then
+  elseif isPlayer ~= true and units["mobs"][name] then
     local ret = units["mobs"][name]
     return ret.class, ret.level, ret.elite, nil, ret.guild
   elseif active then