Merge #9964: Add const to methods that do not modify the object for which it is called

6e8c48dc5 Add const to methods that do not modify the object for which it is called (practicalswift)

Pull request description:

Tree-SHA512: a6888111ba16fb796e320e60806e1a77d36f545989b5405dc7319992291800109eab0b8e8c286b784778f41f1ff5289e7cb6b4afd7aec77f385fbcafc02cffc1

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;
     }