nestegg: fix track_number uint64->uint32 warnings

ne_read_block/ne_find_cue_position_for_track/nestegg_get_cue_point
in the use of ne_map_track_number_to_index
+ add a check to ensure it doesn't exceed the type bounds

fixes:
./third_party/nestegg/src/nestegg.c|1322| warning C4244: 'function' :
conversion from 'uint64_t' to 'unsigned int', possible loss of data

Change-Id: I3703d739dcf9a2d4d8e2b704e957e5e3fd80dca0