Add const to methods that do not modify the object for which it is called

src/streams.h

@@ -332,7 +332,7 @@ public:
     //
     bool eof() const             { return size() == 0; }
     CDataStream* rdbuf()         { return this; }
-    int in_avail()               { return size(); }
+    int in_avail() const         { return size(); }
 
     void SetType(int n)          { nType = n; }
     int GetType() const          { return nType; }
@@ -648,7 +648,7 @@ public:
     }
 
     // return the current reading position
-    uint64_t GetPos() {
+    uint64_t GetPos() const {
         return nReadPos;
     }