reset prev_prefix at the entry of cs_disasm_ex(). this fixes a nasty segfault bug
diff --git a/cs.c b/cs.c
index c2ed6bd..12af4ae 100644
--- a/cs.c
+++ b/cs.c
@@ -309,6 +309,9 @@
 
 	handle->errnum = CS_ERR_OK;
 
+	// reset previous prefix for X86
+	handle->prev_prefix = 0;
+
 	memset(insn_cache, 0, sizeof(insn_cache));
 
 	while (size > 0) {