Try calling try_lock again

Author: JDevlieghere

lldb/unittests/API/SBMutexTest.cpp

@@ -38,6 +38,7 @@ TEST_F(SBMutexTest, LockTest) {
     lldb::SBMutex lock = target.GetAPIMutex();
 
     ASSERT_TRUE(lock.try_lock());
+    ASSERT_FALSE(lock.try_lock());
     lock.unlock();
 
     std::lock_guard<lldb::SBMutex> lock_guard(lock);