common: add missing consts

Adding const was necessary to allow calling
the functions on constant objects.

src/common/tvgArray.h

@@ -59,7 +59,7 @@ struct Array
         data[count++] = element;
     }
 
-    void push(Array<T>& rhs)
+    void push(const Array<T>& rhs)
     {
         if (rhs.count == 0) return;
         grow(rhs.count);

src/common/tvgInlist.h

@@ -100,7 +100,7 @@ struct Inlist
         if (element == tail) tail = element->prev;
     }
 
-    bool empty()
+    bool empty() const
     {
         return head ? false : true;
     }