Catch libjpeg errors in tjDecompressToYUV2()

Catch libjpeg errors in tjDecompressToYUV2()

Even though tjDecompressToYUV2() is mostly just a wrapper for
tjDecompressToYUVPlanes(), tjDecompressToYUV2() still calls
jpeg_read_header(), so it needs to properly set up the libjpeg error
handler prior to making this call.  Otherwise, under very esoteric (and
arguably incorrect) use cases, a program can call tjDecompressToYUV2()
without first checking the JPEG header using tjDecompressHeader3(), and
if the header is corrupt, tjDecompressToYUV2() will abort without
triggering an error.

Fixes #72