Show row values in errors in Firebird backend

This is similar to the other backends without special support for bulk
operations: just remember the current row during bulk operations, so
that we could refer to its values if an error happens.

include/soci/firebird/soci-firebird.h

@@ -198,6 +198,7 @@ struct SOCI_FIREBIRD_DECL firebird_statement_backend : details::statement_backen
     long long get_affected_rows() override;
     int get_number_of_rows() override;
     std::string get_parameter_name(int index) const override;
+    int get_row_to_dump() const override { return current_row_; }
 
     std::string rewrite_for_procedure_call(std::string const &query) override;
 
@@ -252,6 +253,11 @@ struct SOCI_FIREBIRD_DECL firebird_statement_backend : details::statement_backen
     std::map <std::string, int> names_;
 
     bool procedure_;
+
+private:
+    // Used during bulk operations to keep track of the row which potentially
+    // resulted in an error.
+    int current_row_ = -1;
 };
 
 struct SOCI_FIREBIRD_DECL firebird_blob_backend : details::blob_backend

src/backends/firebird/statement.cpp

@@ -413,13 +413,13 @@ firebird_statement_backend::execute(int number)
 
         // Here we have to explicitly loop to achieve the
         // effect of inserting or updating with vector use elements.
-        std::size_t rows = static_cast<firebird_vector_use_type_backend*>(uses_[0])->size();
-        for (std::size_t row=0; row < rows; ++row)
+        const int rows = static_cast<firebird_vector_use_type_backend*>(uses_[0])->size();
+        for (current_row_ = 0; current_row_ < rows; ++current_row_)
         {
             // first we have to prepare input parameters
             for (std::size_t col=0; col<usize; ++col)
             {
-                static_cast<firebird_vector_use_type_backend*>(uses_[col])->exchangeData(row);
+                static_cast<firebird_vector_use_type_backend*>(uses_[col])->exchangeData(current_row_);
             }
 
             // then execute query
@@ -437,6 +437,8 @@ firebird_statement_backend::execute(int number)
             // in same query. So here, we know that into elements are not
             // vectors. So, there is no need to fetch data here.
         }
+
+        current_row_ = -1;
     }
     else
     {