Core/Quest: Fix issues reported by static analysis

(cherry picked from commit f1f4005ad8)

# Conflicts:
#	src/server/game/Entities/Unit/Unit.cpp
#	src/server/game/Entities/Unit/Unit.h
#	src/server/game/Handlers/GroupHandler.cpp

src/server/scripts/Commands/cs_wp.cpp

@@ -377,6 +377,12 @@ public:
 
         if (show == "del")
         {
+            if (!arg_id)
+            {
+                handler->SendSysMessage("|cffff33ffERROR: Waypoint script guid not present.|r");
+                return true;
+            }
+
             id = atoi(arg_id);
 
             stmt = WorldDatabase.GetPreparedStatement(WORLD_SEL_WAYPOINT_SCRIPT_ID_BY_GUID);