Strip U+FFFC from status bodies when posting

Fixes #112

Tusker/Models/Draft.swift

@@ -29,6 +29,12 @@ class Draft: Codable, ObservableObject {
             attachments.count > 0
     }
     
+    var textForPosting: String {
+        // when using dictation, iOS sometimes leaves a U+FFFC OBJECT REPLACEMENT CHARACTER behind in the text,
+        // which we want to strip out before actually posting the status
+        text.replacingOccurrences(of: "\u{fffc}", with: "")
+    }
+    
     init(accountID: String) {
         self.id = UUID()
         self.lastModified = Date()

Tusker/Screens/Compose/ComposeView.swift

@@ -197,7 +197,7 @@ struct ComposeView: View {
                 self.isPosting = false
             
             case let .success(uploadedAttachments):
-                let request = Client.createStatus(text: draft.text,
+                let request = Client.createStatus(text: draft.textForPosting,
                                                   contentType: Preferences.shared.statusContentType,
                                                   inReplyTo: draft.inReplyToID,
                                                   media: uploadedAttachments,