reset prev_prefix at the entry of cs_disasm_ex(). this fixes a nasty segfault bug

cs.c

@@ -309,6 +309,9 @@ size_t cs_disasm_ex(csh ud, const uint8_t *buffer, size_t size, uint64_t offset,
 
 	handle->errnum = CS_ERR_OK;
 
+	// reset previous prefix for X86
+	handle->prev_prefix = 0;
+
 	memset(insn_cache, 0, sizeof(insn_cache));
 
 	while (size > 0) {

suite/benchmark.py

@@ -36,6 +36,10 @@ all_tests = (
         )
 
 
+# for debugging
+def to_hex(s):
+    return " ".join("0x" + "{0:x}".format(ord(c)).zfill(2) for c in s) # <-- Python 3 is OK
+
 def get_code(f, size):
     code = f.read(size)
     if len(code) != size:  # reached end-of-file?
@@ -77,12 +81,16 @@ for (arch, mode, comment, syntax) in all_tests:
         cfile.seek(0)
         for i in xrange(3):
             code = get_code(cfile, 128)
+            #print to_hex(code)
+            #print
             cs(md, code)
 
         # start real benchmark
         c_t = 0
         for i in xrange(50000):
             code = get_code(cfile, 128)
+            #print to_hex(code)
+            #print
 
             t1 = time()
             cs(md, code)