AddressBook: use unsigned type for row ID's

Fixes build warnings and may also prevent future headaches.

src/wallet/api/address_book.cpp

@@ -94,7 +94,7 @@ void AddressBookImpl::refresh()
   
 }
 
-bool AddressBookImpl::deleteRow(int rowId) 
+bool AddressBookImpl::deleteRow(std::size_t rowId)
 {
   LOG_PRINT_L2("Deleting address book row " << rowId);
   bool r = m_wallet->m_wallet->delete_address_book_row(rowId);

src/wallet/api/address_book.h

@@ -46,7 +46,7 @@ public:
     void refresh();
     std::vector<AddressBookRow*> getAll() const;
     bool addRow(const std::string &dst_addr , const std::string &payment_id, const std::string &description);
-    bool deleteRow(int rowId);
+    bool deleteRow(std::size_t rowId);
      
     // Error codes. See AddressBook:ErrorCode enum in wallet2_api.h
     std::string errorString() const {return m_errorString;}