properly set the thread title if it contains no messages

app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt

@@ -60,11 +60,15 @@ class ThreadActivity : SimpleActivity() {
 
         ensureBackgroundThread {
             messages = getMessages(threadId)
-            participants = messages.first().participants
+            participants = if (messages.isEmpty()) {
+                getThreadParticipants(threadId)
+            } else {
+                messages.first().participants
+            }
             setupAdapter()
 
             runOnUiThread {
-                supportActionBar?.title = messages.first().getThreadTitle()
+                supportActionBar?.title = participants.getThreadTitle()
             }
         }
         setupButtons()

app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/ArrayList.kt

@@ -0,0 +1,6 @@
+package com.simplemobiletools.smsmessenger.extensions
+
+import android.text.TextUtils
+import com.simplemobiletools.smsmessenger.models.Contact
+
+fun ArrayList<Contact>.getThreadTitle() = TextUtils.join(", ", map { it.name }.toTypedArray())

app/src/main/kotlin/com/simplemobiletools/smsmessenger/models/Message.kt

@@ -1,12 +1,12 @@
 package com.simplemobiletools.smsmessenger.models
 
 import android.provider.Telephony
-import android.text.TextUtils
+import com.simplemobiletools.smsmessenger.extensions.getThreadTitle
 
 data class Message(
     val id: Int, val body: String, val type: Int, val participants: ArrayList<Contact>, val date: Int, val read: Boolean, val thread: Int
 ) : ThreadItem() {
     fun isReceivedMessage() = type == Telephony.Sms.MESSAGE_TYPE_INBOX
 
-    fun getThreadTitle() = TextUtils.join(", ", participants.map { it.name }.toTypedArray())
+    fun getThreadTitle() = participants.getThreadTitle()
 }