Make sure to set a non-zero exit code in case of exception - so the launcher shows up again..

.gitignore

@@ -27,3 +27,4 @@ nbproject
 
 # generated
 /repo/
+/bin/

src/main/java/net/minecraft/launchwrapper/Launch.java

@@ -135,6 +135,7 @@ public class Launch {
             mainMethod.invoke(null, (Object) argumentList.toArray(new String[argumentList.size()]));
         } catch (Exception e) {
             LogWrapper.log(Level.ERROR, e, "Unable to launch");
+            System.exit(1);
         }
     }
 }