Don't accidentally signal multiple exceptions in setThreadPriority()

After signalling an exception due to set_sched_policy() failing (probably
because the thread in question had exited before this function was called), we
proceeded to call setpriority() anyway, and raised *another* exception when it
also failed.  We don't do this any more; we just bail after signalling the first
exception.

Change-Id: I397b6a93c73d3f0870176e26759f2bec33e56205
diff --git a/core/jni/android_util_Process.cpp b/core/jni/android_util_Process.cpp
index f1c1cb9..094b02d 100644
--- a/core/jni/android_util_Process.cpp
+++ b/core/jni/android_util_Process.cpp
@@ -285,6 +285,7 @@
 
     if (rc) {
         signalExceptionForGroupError(env, clazz, errno);
+        return;
     }
 
     if (setpriority(PRIO_PROCESS, pid, pri) < 0) {