Fix some smaller issues with texture/image handling

irr/include/ITexture.h

@@ -182,7 +182,7 @@ public:
 	//! Lock function.
 	/** Locks the Texture and returns a pointer to access the
 	pixels. After lock() has been called and all operations on the pixels
-	are done, you must call unlock().
+	are done, you must call unlock(). Afterwards the pointer becomes invalid.
 	Locks are not accumulating, hence one unlock will do for an arbitrary
 	number of previous locks. You should avoid locking different levels without
 	unlocking in between, though, because only the last level locked will be