Prevent initiailizing su in main thread

This should hopefully fix #113.

mobile/src/main/java/be/mygod/vpnhotspot/util/RootSession.kt

@@ -2,6 +2,7 @@ package be.mygod.vpnhotspot.util
 
 import android.os.Handler
 import android.os.HandlerThread
+import android.os.Looper
 import androidx.core.os.postDelayed
 import com.topjohnwu.superuser.Shell
 import timber.log.Timber
@@ -67,6 +68,12 @@ class RootSession : AutoCloseable {
 
     class UnexpectedOutputException(msg: String, val result: Shell.Result) : RuntimeException(msg)
 
+    init {
+        check(Looper.getMainLooper().thread != Thread.currentThread()) {
+            "Unable to initialize shell in main thread" // https://github.com/topjohnwu/libsu/issues/33
+        }
+    }
+
     private val shell = Shell.newInstance("su")
     private val stdout = ArrayList<String>()
     private val stderr = ArrayList<String>()