Hide compose progress bar while there is no progress

On iOS 15, the progress bar displays a little bit of progress even at 0

Tusker/Screens/Compose/ComposeView.swift

@@ -58,8 +58,10 @@ struct ComposeView: View {
                 }
             }
             
+            if postProgress > 0 {
                 // can't use SwiftUI.ProgressView because there's no UIProgressView.Style.bar equivalent, see FB8587149
                 WrappedProgressView(value: postProgress, total: postTotalProgress)
+            }
             
             autocompleteSuggestions
         }