Fix sbt hangs with invalid build.sbt and --batch

When sbt is starting up and there is an error with the build loading, we
need to read input from the user to determine to restart the build or
not. What is tricky is that there are potentially two sources of input:
thin clients connected through the boot server socket and the actual sbt
console process. If there are not connected thin clients and no system
console is available, we should return -1 in System.in.read, which will
cause sbt to exit.

internal/util-logging/src/main/scala/sbt/internal/util/Terminal.scala

@@ -179,6 +179,7 @@ trait Terminal extends AutoCloseable {
 }
 
 object Terminal {
+  val NO_BOOT_CLIENTS_CONNECTED: Int = -2
   // Disable noisy jline log spam
   if (System.getProperty("sbt.jline.verbose", "false") != "true")
     jline.internal.Log.setOutput(new PrintStream(_ => {}, false))
@@ -618,6 +619,11 @@ object Terminal {
                 if (running.get) {
                   inputStream.read match {
                     case -1 =>
+                    case `NO_BOOT_CLIENTS_CONNECTED` =>
+                      if (System.console == null) {
+                        result.put(-1)
+                        running.set(false)
+                      }
                     case i =>
                       result.put(i)
                       running.set(false)

main-command/src/main/java/sbt/internal/BootServerSocket.java

@@ -216,6 +216,7 @@ public class BootServerSocket implements AutoCloseable {
       new InputStream() {
         @Override
         public int read() {
+          if (clientSockets.isEmpty()) return Terminal.NO_BOOT_CLIENTS_CONNECTED();
           try {
             synchronized (needInput) {
               needInput.set(true);