Fix the bug where last 7 bits are not processed.

Test case:
$ echo -n aaaa | ./heatshrink -w4 -l2 | ./heatshrink -dw4 -l2 | hexdump -C

expected output:
00000000  61 61 61 61                                       |aaaa|
00000004

bug:
00000000  61                                                |a|
00000001

Conflicts:
	heatshrink_decoder.c