Allow unrecognized options in config file

Prior to this commit, Bisq's new `Config` infrastructure would throw an
exception on encountering an unrecognized option in the
`bisq.properties` config file and the Bisq application would handle this
by reporting an error at the command line indicating that the given
option was not recognized.

For example, given a bisq.properties file that reads as follows:

    $ cat $APP_DATA_DIR/bisq.properties
    bogus=42

running Bisq would exit with the following error message:

    $ java -jar bisq.jar
    error: problem parsing option 'bogus': bogus is not a recognized option.

This was reasonable enough behavior, but it had two problems. The first
is that the error message did not indicate to the user that the
unrecognized option was found in the config file as opposed to the
command line. Users unfamiliar with the config file might not know to
look there to eliminate or fix the offending option. The second problem
surfaced when testing the Windows executable build for the v1.2.6
release. When such an error was encountered, the executable would just
fail silently, reporting nothing to the user.

Both of these problems should be addressed on their own, i.e. option
parsing errors should report to the user whether the offending option
was at the command line or in the config file, and our packaged
executables should never just fail silently if we can avoid it.

However, this change does not address either of these problems directly.
It rather avoids the problems completely by relaxing config file
parsing to silently allow unrecognized options. This behavior mimics
prior (pre-`Config`) Bisq versions, and it also follows suit with
Bitcoin Core's own config file processing.

This fixes #3966, which surfaced this problem. In that particular issue,
an option line had somehow been added to the user's bisq.properties
config file that consisted of an option key containing 452 octal null
characters (\u0000) followed by an equals sign and an empty option
value. It is unknown how this bogus option was ever added to the user's
config file in the first place, but on the chance that previous Bisq
versions somehow added this, the changes in this commit ensure that such
entries will not cause affected users' Bisq applications to silently
fail in versions 1.2.6 and beyond.

common/src/main/java/bisq/common/config/Config.java

@@ -612,6 +612,12 @@ public Config(String defaultAppName, File defaultUserDataDir, String... args) {
             OptionSet cliOpts = parser.parse(args);
             options.addOptionSet(cliOpts);
 
+            // Option parsing is strict at the command line, but we relax it now for any
+            // subsequent config file processing. This is for compatibility with pre-1.2.6
+            // versions that allowed unrecognized options in the bisq.properties config
+            // file and because it follows suit with Bitcoin Core's config file behavior.
+            parser.allowsUnrecognizedOptions();
+
             // Parse config file specified at the command line only if it was specified as
             // an absolute path. Otherwise, the config file will be processed later below.
             File configFile = null;

common/src/test/java/bisq/common/config/ConfigTests.java

@@ -113,6 +113,17 @@ public void whenUnrecognizedOptionIsSet_thenConfigExceptionIsThrown() {
         configWithOpts(opt("bogus"));
     }
 
+    @Test
+    public void whenUnrecognizedOptionIsSetInConfigFile_thenNoExceptionIsThrown() throws IOException {
+        File configFile = File.createTempFile("bisq", "properties");
+        try (PrintWriter writer = new PrintWriter(configFile)) {
+            writer.println(new ConfigFileOption("bogusOption", "bogusValue"));
+            writer.println(new ConfigFileOption(APP_NAME, "BisqTest"));
+        }
+        Config config = configWithOpts(opt(CONFIG_FILE, configFile.getAbsolutePath()));
+        assertThat(config.appName, equalTo("BisqTest"));
+    }
+
     @Test
     public void whenOptionFileArgumentDoesNotExist_thenConfigExceptionIsThrown() {
         exceptionRule.expect(ConfigException.class);