Fix: Loading an invalid image causes a crash

[aoyako]

Platform: Linux Fix the issue when Solar crashes with a segmentation fault on loading an invalid image file (.png, .jpg, .bmp).

Steps to reproduce:

1. Create an empty file with the extension .png (empty.png)
2. Put the following line in the new project's main.lua local background = display.newImageRect("empty.png", 600, 600)

Expected behavior:

Runtime Error is reported.

Actual behavior:

Solar crashed, leaving a log

libpng error: Read Error
Segmentation fault

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