Decompressors: fix header validation in unlzma.c

From: Lasse Collin <lasse.collin@xxxxxxxxxxx>

Validation of header.pos calls error() but doesn't make the function
return to indicate an error to the caller.  Instead the decoding is
attempted with invalid header.pos.  This fixes it.

Signed-off-by: Lasse Collin <lasse.collin@xxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/unlzma.c
+++ b/xen/common/unlzma.c
@@ -568,8 +568,10 @@ STATIC int INIT unlzma(unsigned char *bu
 		((unsigned char *)&header)[i] = *rc.ptr++;
 	}
 
-	if (header.pos >= (9 * 5 * 5))
+	if (header.pos >= (9 * 5 * 5)) {
 		error("bad header");
+		goto exit_1;
+	}
 
 	mi = 0;
 	lc = header.pos;