fix: Use Isolate::TryGetCurrent()

Isolate::GetCurrent() is not supposed to return null; if there is no
current isolate it's supposed to crash. Since we are checking for null
right after, I think we want TryGetCurrent() here.

Author: ptomato

test-app/runtime/src/main/cpp/com_tns_Runtime.cpp

@@ -293,7 +293,7 @@ extern "C" JNIEXPORT jint Java_com_tns_Runtime_getPointerSize(JNIEnv* env, jobje
 }
 
 extern "C" JNIEXPORT jint Java_com_tns_Runtime_getCurrentRuntimeId(JNIEnv* _env, jobject obj) {
-    Isolate* isolate = Isolate::GetCurrent();
+    Isolate* isolate = Isolate::TryGetCurrent();
     if (isolate == nullptr) {
         return -1;
     }