Don't print empty lines to SimpleConsole.

Summary:
If an empty builder is passed to
SimpleConsoleEventBusListener.printLines return rather than printing
an empty line to the console.

Test Plan:
0) buck test --all
1) buckd
2) buck build buck
3) check that no empty lines are printed by 2

src/com/facebook/buck/event/listener/SimpleConsoleEventBusListener.java

diff --git a/src/com/facebook/buck/event/listener/SimpleConsoleEventBusListener.java b/src/com/facebook/buck/event/listener/SimpleConsoleEventBusListener.java
index 13df908..387c996 100644
--- a/src/com/facebook/buck/event/listener/SimpleConsoleEventBusListener.java
+++ b/src/com/facebook/buck/event/listener/SimpleConsoleEventBusListener.java
@@ -117,6 +117,10 @@
     // Print through the {@code DirtyPrintStreamDecorator} so printing from the simple console
     // is considered to dirty stderr and stdout and so it gets synchronized to avoid interlacing
     // output.
-    console.getStdErr().println(Joiner.on("\n").join(lines.build()));
+    ImmutableList<String> stringList = lines.build();
+    if (stringList.size() == 0) {
+      return;
+    }
+    console.getStdErr().println(Joiner.on("\n").join(stringList));
   }
 }