Objects with missing sprite do not load at all.

SuperTux Version

v0.6.3-1204-g3bb35a1c1

System Information

Linux 64-bit (i think)

Expected Behavior

Objects that have a missing sprite load with their default sprite. I believe this was a retrocompatibility measure to prevent the screen from getting spammed with missing textures.

Actual Behavior

Objects that have a missing sprite do not load at all.

Steps To Reproduce Actual Behavior

Make a level with an object that has a missing texture. (by removing an image, or setting the image link to be spam in the txt file)
Dont forget to save.
Restart the game and open the level again. If done correctly the object shouldn't be in the sector at all, and if you set the image file back to a valid image and restart the game the object will reappear.

Additional Information

I was playing some playtester levels and I noticed a lantern that's supposed to spawn isn't spawning because it used a sprite that was not yet in the game, and because of the compatibility measure mentioned above i was very confused when no lantern spawned at all. I also mentioned this issue here.

Guidelines For Reporting Issues

[X] I have read https://github.com/SuperTux/supertux/blob/master/CONTRIBUTING.md#bug-reports.
[X] I have verified this isn't an issue that's already been reported.
[X] I have verified this isn't a discussion, or an issue about a crash or a feature request, but rather an actual bug ─ that is, the game did something not intended.
[X] I have verified this issue is not about wrong translations (use Transifex for those), or anything unsupported (e.g. third-party add-ons).
[X] In this report, I have only included details about one (1) bug.
[X] If I make a mistake while submitting this report, I agree to use the "Edit" feature to correct it, instead of closing this issue and opening a new one.

SuperTux / supertux