[sfnt] Fix memory leak in png loading.

Reported as

  https://bugs.chromium.org/p/chromium/issues/detail?id=1182552

Memory is allocated and the pointer assigned to `rows` inside a
'setjmp' scope.  This memory must be freed outside the 'setjmp'
scope after a 'longjmp'.  Since `rows` is a local and modified
inside the 'setjmp' scope it must be marked volatile or it will have
an indeterminate value after the 'longjmp'.

* src/sfnt/pngshim.c (Load_SBit_Png): Fix memory leak of `rows`.
2 files changed