liblzma: Add NULL checks to LZMA and LZMA2 properties encoders.

Previously lzma_lzma_props_encode() and lzma_lzma2_props_encode()
assumed that the options pointers must be non-NULL because the
with these filters the API says it must never be NULL. It is
good to do these checks anyway.

src/liblzma/lzma/lzma2_encoder.c

@@ -378,6 +378,9 @@ lzma_lzma2_encoder_memusage(const void *options)
 extern lzma_ret
 lzma_lzma2_props_encode(const void *options, uint8_t *out)
 {
+	if (options == NULL)
+		return LZMA_PROG_ERROR;
+
 	const lzma_options_lzma *const opt = options;
 	uint32_t d = my_max(opt->dict_size, LZMA_DICT_SIZE_MIN);
 

src/liblzma/lzma/lzma_encoder.c

@@ -716,6 +716,9 @@ lzma_lzma_lclppb_encode(const lzma_options_lzma *options, uint8_t *byte)
 extern lzma_ret
 lzma_lzma_props_encode(const void *options, uint8_t *out)
 {
+	if (options == NULL)
+		return LZMA_PROG_ERROR;
+
 	const lzma_options_lzma *const opt = options;
 
 	if (lzma_lzma_lclppb_encode(opt, out))