Fixes on android:

- creating Vulkan context instead of OpenGL
- checking for validity of ENV in wrapper classes
- fix for access to JavaVM from threads

platform/android/thread_jandroid.cpp

@@ -30,17 +30,34 @@
 
 #include "thread_jandroid.h"
 
+#include <android/log.h>
+
 #include "core/os/thread.h"
 
 static JavaVM *java_vm = nullptr;
 static thread_local JNIEnv *env = nullptr;
 
+// The logic here need to improve, init_thread/term_tread are designed to work with Thread::callback
+// Calling init_thread from setup_android_thread and get_jni_env to setup an env we're keeping and not detaching
+// could cause issues on app termination.
+//
+// We should be making sure that any thread started calls a nice cleanup function when it's done,
+// especially now that we use many more threads.
+
 static void init_thread() {
+	if (env) {
+		// thread never detached! just keep using...
+		return;
+	}
+
 	java_vm->AttachCurrentThread(&env, nullptr);
 }
 
 static void term_thread() {
 	java_vm->DetachCurrentThread();
+
+	// this is no longer valid, must called init_thread to re-establish
+	env = nullptr;
 }
 
 void init_thread_jandroid(JavaVM *p_jvm, JNIEnv *p_env) {
@@ -50,9 +67,17 @@ void init_thread_jandroid(JavaVM *p_jvm, JNIEnv *p_env) {
 }
 
 void setup_android_thread() {
-	init_thread();
+	if (!env) {
+		// !BAS! see remarks above
+		init_thread();
+	}
 }
 
 JNIEnv *get_jni_env() {
+	if (!env) {
+		// !BAS! see remarks above
+		init_thread();
+	}
+
 	return env;
 }