We're given a PNG with the width and height fields set to 0.
However, the original CRC is intact.
The CRC is a unique value used to check for the integrity of the preceeding chunk, similar to a hash funciton.
Because of this, we can 'crack' the original dimensions with this:
Sizes are: 0x00 0x00 0x05 0x62 0x00 0x00 0x01 0x6B
Adding this back to the image, we get the original image, containing the flag. [IMAGE HERE]