8054008: Using -XX:-LazyBootClassLoader crashes with ACCESS_VIOLATION on Win 64bit.

Summary: Only enable the assert for current_stack_pointer after stub routines become available.
Reviewed-by: dholmes, roland, lfoltan

src/os_cpu/windows_x86/vm/os_windows_x86.cpp

@@ -635,7 +635,11 @@ void os::setup_fpu() {
 #ifndef PRODUCT
 void os::verify_stack_alignment() {
 #ifdef AMD64
+  // The current_stack_pointer() calls generated get_previous_sp stub routine.
+  // Only enable the assert after the routine becomes available.
+  if (StubRoutines::code1() != NULL) {
     assert(((intptr_t)os::current_stack_pointer() & (StackAlignmentInBytes-1)) == 0, "incorrect stack alignment");
+  }
 #endif
 }
 #endif