Use size_t for lengths in stream objects

Provides safety against them accidentally becoming negative because
of bugs in the calculations.

Also does the same to CharArray and friends as they were strongly
connection to the stream objects.

common/rdr/RandomStream.h

@@ -39,14 +39,14 @@ namespace rdr {
     RandomStream();
     virtual ~RandomStream();
 
-    int pos();
+    size_t pos();
 
   protected:
-    int overrun(int itemSize, int nItems, bool wait);
+    size_t overrun(size_t itemSize, size_t nItems, bool wait);
 
   private:
     U8* start;
-    int offset;
+    size_t offset;
 
     static unsigned int seed;
 #ifdef RFB_HAVE_WINCRYPT