Segmentation fault of firebase while rotating orientation of IOS

Hey,
I had few cases of segmentation fault of Firebase on my ios crash log. Based on it, it was because of incorrect re-initalization of the firebase while screen was being rotated int he application.

### Please fill in the following fields:
Firebase C++ SDK version: 6.7
Firebase plugins in use (Auth, Database, etc.): FirebaseAnalytics, FirebaseCore, FirebaseInstanceID
Additional SDKs you are using (Facebook, AdMob, etc.): qt 5.13.2 + qfirebase lib to use firebase with a qml https://github.com/Larpon/QtFirebase
Platform you are using the SDK on (Mac, Windows, or Linux): Mac
Platform you are targeting (iOS, Android, and/or desktop): IOS

### Please describe the issue here:
Looks like it is related to changing orientation of app, during that time firebase is re-initialised and mutex is not correctly handled

Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler [81193]
Triggered by Thread: 0

```
Thread 0 name:
Thread 0 Crashed:
0 libsystem_pthread.dylib 0x0000000190a693fc pthread_mutex_lock$VARIANT$mp + 0 (pthread_mutex.c:1491)
1 app 0x00000001025fda80 std::__1::__tree_const_iterator, std::__1::allocator >, flatbuffers::EnumVal*>, std::__1::__tree_node, std::__1::allocator >, flatbuffers::EnumVal*>, void*>*, long> std::__1::__tree, std::__1::allocator >, flatbuffers::EnumVal*>, std::__1::__map_value_compare, std::__1::allocator >, std::__1::__value_type, std::__1::allocator >, flatbuffers::EnumVal*>, std::__1::less, std::__1::allocator > >, true>, std::__1::allocator, std::__1::allocator >, flatbuffers::EnumVal*> > >::find, std::__1::allocator > >+ 1694336 (std::__1::basic_string, std::__1::allocator > const&) const + 12
2 app 0x0000000102601110 std::__1::enable_if<(__is_forward_iterator, std::__1::allocator >*>::value) && (is_constructible, std::__1::allocator >, std::__1::iterator_traits, std::__1::allocator >*>::reference>::value), void>::type std::__1::vector, std::__1::allocator >, std::__1::allocator, std::__1::allocator > > >::assign, std::__1::allocator >*>+ 1708304 (std::__1::basic_string, std::__1::allocator >*, std::__1::basic_string, std::__1::allocator >*) + 36
3 app 0x00000001025fcc18 firebase::analytics::Initialize+ 1690648 (firebase::App const&) + 84
4 app 0x000000010252bb9c QtFirebaseAnalytics::init() + 834460 (qtfirebaseanalytics.cpp:0)
5 app 0x00000001034ca364 QQmlExpression::QQmlExpression+ 17212260 () + 2224
6 app 0x000000010252ab5c QtFirebase::requestInit() + 830300 (qtfirebase.cpp:0)
7 app 0x00000001034ca364 QQmlExpression::QQmlExpression+ 17212260 () + 2224
8 app 0x00000001034cec90 QWindowSystemInterfacePrivate::GeometryChangeEvent::GeometryChangeEvent+ 17230992 (QWindow*, QRect const&) + 120
9 app 0x00000001034c2e9c QObject::event+ 17182364 (QEvent*) + 80
10 app 0x00000001034a26f8 QObject::userData+ 17049336 (unsigned int) const + 124
11 app 0x00000001034a22cc QVector::resize+ 17048268 (int) + 204
12 app 0x00000001034e7bc4 QEucJpCodec::QEucJpCodec+ 17333188 () + 932
13 app 0x000000010353c9d8 QIPAddressUtils::parseIp4Internal+ 17680856 (unsigned int&, char const*, bool) + 620
14 CoreFoundation 0x0000000190cd0e1c __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 28 (CFRunLoop.c:1766)
15 CoreFoundation 0x0000000190cd0b58 __CFRunLoopDoTimer + 880 (CFRunLoop.c:2357)
16 CoreFoundation 0x0000000190cd0228 __CFRunLoopDoTimers + 276 (CFRunLoop.c:2512)
17 CoreFoundation 0x0000000190ccb364 __CFRunLoopRun + 1920 (CFRunLoop.c:0)
18 CoreFoundation 0x0000000190cca8bc CFRunLoopRunSpecific + 464 (CFRunLoop.c:3192)
19 GraphicsServices 0x000000019ab36328 GSEventRunModal + 104 (GSEvent.c:2246)
20 UIKitCore 0x0000000194d606d4 UIApplicationMain + 1936 (UIApplication.m:4753)
21 app 0x0000000102606df0 qt_main_wrapper + 820
22 libdyld.dylib 0x0000000190b55460 start + 4
```

### Please answer the following, if applicable:
Have you been able to reproduce this issue with just the Firebase C++ quickstarts (this GitHub project)? Crash happent to a user, but based on crash log it was during app being rotated and Fireabe was being reinitalized.

What's the issue repro rate? (eg 100%, 1/5 etc) Wasn't able to repro myself so would say "low".