Kernel: Make Lock::lock() assert early that we're not in the scheduler

The scheduler is not allowed to take locks, so if that's happening,
we want to make that clear instead of crashing with the more general
"Interrupts disabled while trying to take Lock" error.

Kernel/Lock.cpp

@@ -2,12 +2,12 @@
 
 void Lock::lock()
 {
+    ASSERT(!Scheduler::is_active());
     if (!are_interrupts_enabled()) {
         kprintf("Interrupts disabled when trying to take Lock{%s}\n", m_name);
         dump_backtrace();
         hang();
     }
-    ASSERT(!Scheduler::is_active());
     for (;;) {
         if (CAS(&m_lock, 1, 0) == 0) {
             if (!m_holder || m_holder == current) {