[Zion] Zero-out thread fx_data_ on creation.

zion/object/thread.cpp

@@ -51,6 +51,9 @@ Thread::Thread(Process& proc, uint64_t tid)
   if (reinterpret_cast<uint64_t>(fx_data_) & 0x8) {
     fx_data_ += 8;
   }
+  for (uint16_t i = 0; i < 512; i++) {
+    fx_data_[i] = 0;
+  }
 }
 
 uint64_t Thread::pid() const { return process_.id(); }