Avoid uninitialized value in call_once implementation.

There is a path in which the guard_result_ member is
not initialized; this is benign as the code makes
sure that it only accesses an initialized state.

Static analysis tools (such as clang-tidy) might not
see that however, so to make them happy, initialize
that value.

PiperOrigin-RevId: 516876319
Change-Id: I1bd2e97ad9e1daaa1397f306df993de13f7e684e

absl/base/call_once.h

@@ -123,7 +123,7 @@ class SchedulingHelper {
 
  private:
   base_internal::SchedulingMode mode_;
-  bool guard_result_;
+  bool guard_result_ = false;
 };
 
 // Bit patterns for call_once state machine values.  Internal implementation