Fixes a thread safety issue with currentMessage being out of sync.

messaginginapp/src/main/java/io/customer/messaginginapp/gist/presentation/GistModalManager.kt

@@ -14,23 +14,25 @@ internal class GistModalManager : GistListener {
     }
 
     internal fun showModalMessage(message: Message, position: MessagePosition? = null): Boolean {
-        currentMessage?.let { currentMessage ->
-            Log.i(
-                GIST_TAG,
-                "Message ${message.messageId} not shown, ${currentMessage.messageId} is already showing."
-            )
-            return false
-        }
+        synchronized(this) {
+            currentMessage?.let { currentMessage ->
+                Log.i(
+                    GIST_TAG,
+                    "Message ${message.messageId} not shown, ${currentMessage.messageId} is already showing."
+                )
+                return false
+            }
 
-        Log.i(GIST_TAG, "Showing message: ${message.messageId}")
-        currentMessage = message
+            Log.i(GIST_TAG, "Showing message: ${message.messageId}")
+            currentMessage = message
 
-        val intent = GistModalActivity.newIntent(GistSdk.application)
-        intent.flags = Intent.FLAG_ACTIVITY_NEW_TASK
-        intent.putExtra(GIST_MESSAGE_INTENT, Gson().toJson(message))
-        intent.putExtra(GIST_MODAL_POSITION_INTENT, position?.toString())
-        GistSdk.application.startActivity(intent)
-        return true
+            val intent = GistModalActivity.newIntent(GistSdk.application)
+            intent.flags = Intent.FLAG_ACTIVITY_NEW_TASK
+            intent.putExtra(GIST_MESSAGE_INTENT, Gson().toJson(message))
+            intent.putExtra(GIST_MODAL_POSITION_INTENT, position?.toString())
+            GistSdk.application.startActivity(intent)
+            return true
+        }
     }
 
     internal fun dismissActiveMessage() {