plaintext mime type fix - Don't attempt to extract HTML content from plaintext, this will remove lines and break changedetection (#391)

changedetectionio/fetch_site_status.py

@@ -118,6 +118,8 @@ class perform_site_check():
             if is_html:
                 # CSS Filter, extract the HTML that matches and feed that into the existing inscriptis::get_text
                 html_content = fetcher.content
+                if not fetcher.headers.get('Content-Type', '') == 'text/plain':
+
                     if has_filter_rule:
                         # For HTML/XML we offer xpath as an option, just start a regular xPath "/.."
                         if css_filter_rule[0] == '/':
@@ -128,6 +130,9 @@ class perform_site_check():
 
                     # get_text() via inscriptis
                     stripped_text_from_html = get_text(html_content)
+                else:
+                    # Don't run get_text or xpath/css filters on plaintext
+                    stripped_text_from_html = html_content
 
             # Re #340 - return the content before the 'ignore text' was applied
             text_content_before_ignored_filter = stripped_text_from_html.encode('utf-8')