Fix narrowing conversion warning in row::raw()

Fixes #20

Author: ashtum

include/lazycsv.hpp

@@ -459,7 +459,7 @@ class parser
         std::string_view
         raw() const
         {
-            return { begin_, end_ - begin_ };
+            return { begin_, static_cast<std::size_t>(end_ - begin_) };
         }
 
         template<typename... Indexes>

test/main.cpp

@@ -57,6 +57,8 @@ TEST_CASE("parse basic.csv with mmap_source and use cells function")
         { "A3", "B3", "C3", "D3" }
     };
 
+    REQUIRE_EQ("A0,B0,C0,D0", parser.header().raw());
+
     const auto [a, b, c, d] = parser.header().cells(0, 1, 2, 3);
     auto header_cells       = expected_rows.at(0);
     REQUIRE_EQ(header_cells[0], a.raw());