8541: Crash following update: addon permission issue blocks re-starting gramps

There were two issues:

1. attempting to read a new addon file that wasn't readable
   threw an exception, aborted updating addons

2. global error catching didn't properly handle error code
   from an OSError

gramps/gen/plug/_pluginreg.py

@@ -1096,7 +1096,13 @@ class PluginRegister(object):
                 continue
             lenpd = len(self.__plugindata)
             full_filename = os.path.join(dir, filename)
+            try:
                 fd = io.open(full_filename, "r", encoding='utf-8')
+            except Exception as msg:
+                print(_('ERROR: Failed reading plugin registration %(filename)s') % \
+                            {'filename' : filename})
+                print(msg)
+                continue
             stream = fd.read()
             fd.close()
             if os.path.exists(os.path.join(os.path.dirname(full_filename),

gramps/gui/grampsgui.py

@@ -383,7 +383,7 @@ def __startgramps(errors, argparser):
                       % e.code, exc_info=True)
     except OSError as e:
         quit_now = True
-        exit_code = e[0] or 1
+        exit_code = e.errno or 1
         try:
             fn = e.filename
         except AttributeError: