liblzma: Make Valgrind happier with optimized (gcc -O2) liblzma.

When optimizing, GCC can reorder code so that an uninitialized
value gets used in a comparison, which makes Valgrind unhappy.
It doesn't happen when compiled with -O0, which I tend to use
when running Valgrind.

Thanks to Rich Prohaska. I remember this being mentioned long
ago by someone else but nothing was done back then.

src/liblzma/lz/lz_encoder.c

@@ -541,4 +541,7 @@
 		next->coder->lz.code = NULL;
 		next->coder->lz.end = NULL;
 
+		// mf.size is initialized to silence Valgrind
+		// when used on optimized binaries (GCC may reorder
+		// code in a way that Valgrind gets unhappy).
 		next->coder->mf.buffer = NULL;
@@ -544,4 +547,5 @@
 		next->coder->mf.buffer = NULL;
+		next->coder->mf.size = 0;
 		next->coder->mf.hash = NULL;
 		next->coder->mf.son = NULL;
 		next->coder->mf.hash_count = 0;