Fixed assert on android when not using default app instance and trying to auth.

Github issue: firebase/quickstart-unity#461

PiperOrigin-RevId: 268992783

Author: markchandler

app/src/app_common.cc

@@ -301,6 +301,10 @@ App* FindAppByName(const char* name) {
 App* GetDefaultApp() { return g_default_app; }
 
 App* GetAnyApp() {
+  if (g_default_app) {
+    return g_default_app;
+  }
+
   MutexLock lock(g_app_mutex);
   if (g_apps && !g_apps->empty()) {
     return g_apps->begin()->second->app;

auth/src/android/credential_android.cc

@@ -20,6 +20,7 @@
 #include <cstring>
 
 #include "app/src/assert.h"
+#include "app/src/app_common.h"
 #include "app/src/build_type_generated.h"
 #include "app/src/embedded_file.h"
 #include "app/src/include/firebase/app.h"
@@ -310,9 +311,8 @@ void ReleaseCredentialClasses(JNIEnv* env) {
 }
 
 static JNIEnv* GetJniEnv() {
-  // The default App must always exist, and the JNI environment is the same
-  // regardless of App.
-  App* app = App::GetInstance();
+  // The JNI environment is the same regardless of App.
+  App* app = app_common::GetAnyApp();
   FIREBASE_ASSERT(app != nullptr);
   return app->GetJNIEnv();
 }