a possible null pointer dereference?

Hi all,
There is a possible null pointer dereference issue found by Qihoo360 CodeSafe Team.
Details as bellow:

function FLAC__metadata_simple_iterator_get_block() may return a null pointer:
https://github.com/libretro/4do-libretro/blob/9d76c93c140d227211411b351ad03b8252d21a3a/deps/flac-1.3.2/src/libFLAC/metadata_iterators.c#L647-L674

before use the return value of function FLAC__metadata_simple_iterator_get_block(), there is no check against null:
https://github.com/libretro/4do-libretro/blob/9d76c93c140d227211411b351ad03b8252d21a3a/deps/flac-1.3.2/src/libFLAC/metadata_iterators.c#L309

since in function FLAC__metadata_simple_iterator_get_block(), there is a check against null pointer (0), and an ERROR status (FLAC__METADATA_SIMPLE_ITERATOR_STATUS_MEMORY_ALLOCATION_ERROR) is set to 'iterator->status' when the return value is a null pointer, it will be better if a checking against null (either by checking the pointer or by the status is ok).

Cheers
Qihoo360 CodeSafe Team

Start in deps/flac-1.3.2/src/libFLAC/metadata_iterators.c, examining FLAC__metadata_simple_iterator_get_block() at lines 647-674 and its use near line 309. Trace how the iterator status and returned block are handled, then verify that the null-return path is safely covered without changing normal metadata iteration.