Avoid doing any work when unwinding stack traces with 0 or 1 frame

llvm-svn: 202837
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_win.cc b/compiler-rt/lib/sanitizer_common/sanitizer_win.cc
index 162f37d..21f92b3 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_win.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_win.cc
@@ -417,6 +417,7 @@
 }
 
 void StackTrace::SlowUnwindStack(uptr pc, uptr max_depth) {
+  CHECK_GE(max_depth, 2);
   // FIXME: CaptureStackBackTrace might be too slow for us.
   // FIXME: Compare with StackWalk64.
   // FIXME: Look at LLVMUnhandledExceptionFilter in Signals.inc