[FIX] account_statement_import_sheet_file: Prevent negative index in …

…parser header

When importing an Excel file with a header and the field header_lines_skip_count is set to its default value (0), the header is retrieved using the -1 index (the last row).
complementary to commit 13285ab

account_statement_import_sheet_file/models/account_statement_import_sheet_parser.py

@@ -179,7 +179,10 @@ def _parse_lines(self, mapping, data_file, currency_code):
             csv_or_xlsx = reader(StringIO(decoded_file), **csv_options)
         header = False
         if not mapping.no_header:
-            header_line = mapping.header_lines_skip_count - 1
+            header_line = mapping.header_lines_skip_count
+            # prevent negative indexes
+            if header_line > 0:
+                header_line -= 1
             if isinstance(csv_or_xlsx, tuple):
                 header = [
                     str(value).strip()