Avoid breaking already fixed headers

import re

import argparse

index_pattern = re.compile(r"^.. index:: (fix|pair_style)\s+([a-zA-Z0-9/_]+)$")

pattern = re.compile(r"^(fix|pair_style)\s+([a-zA-Z0-9/_]+)\s+command$")

parser = argparse.ArgumentParser(description='Fixup headers in docs')

            if line.startswith("Syntax"):

                break

            m = index_pattern.match(line)

            if not m:

                m = pattern.match(line)

            if m:

                command_type = m.group(1)

                style        = m.group(2)

                if style not in styles:

                    styles.append(style)

                base_name = '/'.join(style.split('/')[0:-1])

                ext = style.split('/')[-1]

                if ext not in ('omp', 'intel', 'kk', 'gpu', 'opt'):

                    if style not in headings:

                        headings[style] = []

                else:

                elif style not in headings[base_name]:

                    headings[base_name].append(style)

        # write new header

            print(file=writer)

            if len(variants) > 0:

                print("Accelerator Styles: ", end="", file=writer)

                print("Accelerator Variants: ", end="", file=writer)

                print(", ".join([f"*{v}*" for v in variants]), file=writer)

            print(file=writer)