help parameter now returns 0

Fixes: 283071548
Test: `adb shell am help` returns 0.
Change-Id: I38fb725d7a3193a35d7629fdb41f0c68422f6a8d

services/core/java/com/android/server/am/ActivityManagerShellCommand.java

@@ -229,6 +229,9 @@ final class ActivityManagerShellCommand extends ShellCommand {
         final PrintWriter pw = getOutPrintWriter();
         try {
             switch (cmd) {
+                case "help":
+                    onHelp();
+                    return 0;
                 case "start":
                 case "start-activity":
                     return runStartActivity(pw);