liblzma: Make lzma_lz_decoder_init() safe to reinit after alloc failure

If memory allocation fails and the resulting coder state is reused,
ensure that memory allocation is attempted again. However, coders that
are initialized via lzma_next_filter_init() shouldn't be reinitialized
after failure; they should be cleaned up with lzma_next_end().

Reported-by: GitHub user christos-cantina-security (christos-spearbit)

src/liblzma/lz/lz_decoder.c

@@ -278,6 +278,7 @@ lzma_lz_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
 
 	// Allocate and initialize the dictionary.
 	if (coder->dict.size != alloc_size) {
+		coder->dict.size = 0;
 		lzma_free(coder->dict.buf, allocator);
 
 		// The LZ_DICT_EXTRA bytes at the end of the buffer aren't