Properly initialize class loader on Android

https://github.com/OpenRCT2/OpenRCT2/pull/20502 changed how startup is
handled. This affected Android as well and changed AndroidClassLoader to
be initialized statically, but this turns out to be problematic due to
JVM not being fully initialized in our context by this time.

To fix this, move AndroidClassLoader initialization to JNI_OnLoad call,
where JVM is fully available.

Additionally, guard against multiple calls to JNI_OnLoad, an issue
present on Linux-like systems (including Android).

distribution/changelog.txt

@@ -10,6 +10,7 @@
 - Fix: [#18199] Dots in the game save's name no longer get truncated.
 - Fix: [#19722] “Forbid tree removal” restriction doesn't forbid removal of large scenery tree items.
 - Fix: [#20356] Cannot set tertiary colour on small scenery.
+- Fix: [#20679] Android: game crashes at launch.
 - Fix: [#20737] Spent money in player window underflows when getting refunds.
 - Fix: [#20778] [Plugin] Incorrect target api when executing custom actions.
 - Fix: [#20807] Tertiary colour not copied with small scenery.

src/openrct2/platform/Platform.Android.cpp

@@ -27,7 +27,9 @@ AndroidClassLoader::~AndroidClassLoader()
 jobject AndroidClassLoader::_classLoader;
 jmethodID AndroidClassLoader::_findClassMethod;
 
-static std::shared_ptr<AndroidClassLoader> acl = std::make_shared<AndroidClassLoader>();
+// Initialized in JNI_OnLoad. Cannot be initialized here as JVM is not
+// available until after JNI_OnLoad is called.
+static std::shared_ptr<AndroidClassLoader> acl;
 
 namespace Platform
 {
@@ -181,6 +183,19 @@ namespace Platform
     }
 } // namespace Platform
 
+JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* pjvm, void* reserved)
+{
+    // Due to an issue where JNI_OnLoad could be called multiple times, we need
+    // to make sure it is only initialized once.
+    // https://issuetracker.google.com/issues/220523932
+    // Otherwise JVM complains about jobject-s having incorrect serial numbers.
+    if (!acl)
+    {
+        acl = std::make_shared<AndroidClassLoader>();
+    }
+    return JNI_VERSION_1_6;
+}
+
 AndroidClassLoader::AndroidClassLoader()
 {
     LOG_INFO("Obtaining JNI class loader");