csv: fix last-field-empty error

vlib/encoding/csv/reader_test.v

@@ -120,3 +120,30 @@ fn test_no_line_ending() {
 
 	assert row_count == 2
 }
+
+fn test_last_field_empty() {
+	data := '"name","description","value"\n"one","first","1"\n"two","second",\n'
+	mut csv_reader := csv.new_reader(data)
+
+	mut row_count := 0
+	for {
+    	row := csv_reader.read() or {
+        	break
+    	}
+    	row_count++
+		if row_count == 1 {
+			assert row[0] == 'name'
+			assert row[1] == 'description'
+			assert row[2] == 'value'
+		}
+		if row_count == 2 {
+			assert row[0] == 'one'
+			assert row[1] == 'first'
+			assert row[2] == '1'
+		}
+		if row_count == 3 {
+			assert row[0] == 'two'
+			assert row[1] == 'second'
+		}
+	}
+}