Fix a build error

Add Metadata::Metadata()

Author: wh201906

src/metadata.cpp

@@ -1,6 +1,12 @@
 
 #include "metadata.h"
 
+Metadata::Metadata() :
+    pos(0), len(0), timestamp(0)
+{
+
+}
+
 Metadata::Metadata(qint64 pos, qint64 len, qint64 timestamp) :
     pos(pos), len(len), timestamp(timestamp)
 {

src/metadata.h

@@ -6,6 +6,7 @@
 class Metadata
 {
 public:
+    Metadata();
     Metadata(qint64 pos, qint64 len, qint64 timestamp);
     qint64 pos = 0;
     qint64 len = 0;