fix bug 694111

jbig2_image_compose fails to ensure that the destination rectangle lies entirely within the destination buffer (in the case of the file 3324.pdf.asan.50.2585, this happens due to a huge value for y). Adding a new check which makes sure that...

@ y * dst->stride + leftbyte doesn't overflow
@ x and leftbyte don't overflow to the next line
@ h * dst->stride doesn't overflow
@ all values read are within the destination buffer

The file 3324.pdf.asan.50.2585 also demonstrates a memory leak where the glyph isn't properly released if jbig2_image_compose fails.