png: convert png_read to g_autoptr
png: convert png_read to g_autoptr

Use __attribute__((noinline)) to avoid inlining that causes gcc 12.1.1
to emit a setjmp clobber warning.  This isn't ideal, but the glib wrapper
isn't available in glib 2.56, and we're already dependent on GNU C for
the cleanup attribute.

Signed-off-by: Benjamin Gilbert <55d1d0083477f6dd5757d8929dd3b9e09d80bd84@cs.cmu.edu>

openslide/openslide,openslide/openslide,openslide/openslide,openslide/openslide