Core/Spells: fixed power check for runes when casting spells - these have their own check and don't require the default one

Port From (https://github.com/TrinityCore/TrinityCore/commit/d9c2720393e95c9e0bac5c5d1d95bbdcf94d5c5b)

Source/Game/Spells/Spell.cs

@@ -6663,6 +6663,8 @@ namespace Game.Spells
                     SpellCastResult failReason = CheckRuneCost();
                     if (failReason != SpellCastResult.SpellCastOk)
                         return failReason;
+
+                    continue;
                 }
 
                 // Check power amount