Catch exceptions when Comsol preference does not exist.

This should fix start-up failure with older Comsol installations.
See issue #50.

mph/client.py

@@ -200,16 +200,18 @@ def __init__(self, cores=None, version=None, port=None, host='localhost'):
             java.loadPreferences()
 
             # Override certain settings not useful in headless operation.
-            java.setPreference('updates.update.check', 'off')
-            java.setPreference('tempfiles.saving.warnifoverwriteolder', 'off')
-            java.setPreference('tempfiles.recovery.autosave', 'off')
-            try:
-                # Preference not defined on certain systems, see issue #39.
-                java.setPreference('tempfiles.recovery.checkforrecoveries',
-                                   'off')
-            except Exception:
-                log.debug('Could not turn off check for recovery files.')
-            java.setPreference('tempfiles.saving.optimize', 'filesize')
+            preferences = (
+                ('updates.update.check', 'off'),
+                ('tempfiles.saving.warnifoverwriteolder', 'off'), # issue #50
+                ('tempfiles.recovery.autosave', 'off'),
+                ('tempfiles.recovery.checkforrecoveries', 'off'), # issue #39
+                ('tempfiles.saving.optimize', 'filesize'),
+            )
+            for (name, value) in preferences:
+                try:
+                    java.setPreference(name, value)
+                except Exception:
+                    log.info(f'Preference {name} does not exist.')
 
             # Log that we're done so the start-up time may be inspected.
             log.info('Stand-alone client initialized.')