fix: ignore badly coded user-provided html of older documents (ietf-tools#4845)

Author: rjsparks

ietf/doc/models.py

@@ -550,7 +550,7 @@ def html_body(self, classes=""):
                 html = Path(
                     os.path.join(settings.RFC_PATH, self.canonical_name() + ".html")
                 ).read_text()
-            except IOError:
+            except (IOError, UnicodeDecodeError):
                 return None
         else:
             try:
@@ -560,7 +560,7 @@ def html_body(self, classes=""):
                         self.name + "-" + self.rev + ".html",
                     )
                 ).read_text()
-            except IOError:
+            except (IOError, UnicodeDecodeError):
                 return None
 
         # If HTML was generated by rfc2html, do not return it. Caller