liblzma: Silence two Coverity warnings

lzma_lzma_decoder_memusage() returns UINT64_MAX if lc/lp/pb aren't
valid. alone_decoder.c and lzip_decoder.c didn't check the return
value because in both it is known that lc/lp/pb are valid. Make them
call the _nocheck() variant instead which skips the validation (it
already existed for LZMA2's internal use).

Fixes: Coverity CID 464658
Fixes: Coverity CID 897069

src/liblzma/common/alone_decoder.c

@@ -128,8 +128,10 @@ alone_decode(void *coder_ptr, const lzma_allocator *allocator,
 		lzma_set_ext_size(coder->options, coder->uncompressed_size);
 
 		// Calculate the memory usage so that it is ready
-		// for SEQ_CODER_INIT.
+		// for SEQ_CODER_INIT. We know that lc/lp/pb are valid
-		coder->memusage = lzma_lzma_decoder_memusage(&coder->options)
+		// so we can use the _nocheck variant.
+		coder->memusage
+			= lzma_lzma_decoder_memusage_nocheck(&coder->options)
 				+ LZMA_MEMUSAGE_BASE;
 
 		coder->pos = 0;

src/liblzma/common/lzip_decoder.c

@@ -212,7 +212,8 @@ lzip_decode(void *coder_ptr, const lzma_allocator *allocator,
 		coder->options.pb = LZIP_PB;
 
 		// Calculate the memory usage.
-		coder->memusage = lzma_lzma_decoder_memusage(&coder->options)
+		coder->memusage
+			= lzma_lzma_decoder_memusage_nocheck(&coder->options)
 				+ LZMA_MEMUSAGE_BASE;
 
 		// Initialization is a separate step because if we return

src/liblzma/lzma/lzma_decoder.h

@@ -23,6 +23,12 @@ extern lzma_ret lzma_lzma_decoder_init(lzma_next_coder *next,
 
 extern uint64_t lzma_lzma_decoder_memusage(const void *options);
 
+/// Gets memory usage without validating lc/lp/pb. This is used by LZMA2
+/// decoder, because raw LZMA2 decoding doesn't need lc/lp/pb. Also
+/// alone_decoder.c and lzip_decoder.c use this because there lc/lp/pb
+/// are known to be valid.
+extern uint64_t lzma_lzma_decoder_memusage_nocheck(const void *options);
+
 extern lzma_ret lzma_lzma_props_decode(
 		void **options, const lzma_allocator *allocator,
 		const uint8_t *props, size_t props_size);
@@ -42,11 +48,6 @@ extern bool lzma_lzma_lclppb_decode(
 extern lzma_ret lzma_lzma_decoder_create(
 		lzma_lz_decoder *lz, const lzma_allocator *allocator,
 		const lzma_options_lzma *opt, lzma_lz_options *lz_options);
-
-/// Gets memory usage without validating lc/lp/pb. This is used by LZMA2
-/// decoder, because raw LZMA2 decoding doesn't need lc/lp/pb.
-extern uint64_t lzma_lzma_decoder_memusage_nocheck(const void *options);
-
 #endif
 
 #endif