Count threads after thread-creation while still holding mutex lockrefs/pull/4365/head

The `Mutex` is locked with the `MutexLock` before spawning the thread, so that the thread is prevented from completing (by being blocked on `Mutex`) before the new thread count is obtained. However, the existing bug (introduced in 22e6055) releases `Mutex` before obtaining the new thread count, which allows the thread to run to completion in the meantime.

Also, since the `(thread_count_after_create != starting_count + 1)` condition (line 328) skips the remainder of the `for`-loop body on every iteration, `thread_count_after_join` stays uninitialized.

I believe this is why [this test failed][1] on the macOS CI with this trace:

```
[----------] 1 test from GetThreadCountTest
[ RUN      ] GetThreadCountTest.ReturnsCorrectValue
googletest/test/googletest-port-test.cc:350: Failure
Expected equality of these values:
  thread_count_after_create
    Which is: 1
  starting_count + 1
    Which is: 2

googletest/test/googletest-port-test.cc:351: Failure
Expected equality of these values:
  thread_count_after_join
    Which is: 140493185949400
  starting_count
    Which is: 1

[  FAILED  ] GetThreadCountTest.ReturnsCorrectValue (2 ms)
[----------] 1 test from GetThreadCountTest (2 ms total)
```

[1]: https://github.com/google/googletest/actions/runs/6064919420/job/16453860690?pr=3049

1 files changed, 3 insertions, 3 deletions

diff --git a/googletest/test/googletest-port-test.cc b/googletest/test/googletest-port-test.cc
index e0793ba..8d21026 100644
--- a/googletest/test/googletest-port-test.cc
+++ b/googletest/test/googletest-port-test.cc
@@ -296,7 +296,7 @@ void* ThreadFunc(void* data) {
 TEST(GetThreadCountTest, ReturnsCorrectValue) {
   size_t starting_count;
   size_t thread_count_after_create;
-  size_t thread_count_after_join;
+  size_t thread_count_after_join = 0;
 
   // We can't guarantee that no other thread was created or destroyed between
   // any two calls to GetThreadCount(). We make multiple attempts, hoping that
@@ -316,9 +316,9 @@ TEST(GetThreadCountTest, ReturnsCorrectValue) {
       const int status = pthread_create(&thread_id, &attr, &ThreadFunc, &mutex);
       ASSERT_EQ(0, pthread_attr_destroy(&attr));
       ASSERT_EQ(0, status);
-    }
 
-    thread_count_after_create = GetThreadCount();
+      thread_count_after_create = GetThreadCount();
+    }
 
     void* dummy;
     ASSERT_EQ(0, pthread_join(thread_id, &dummy));