Fixed pasting text sending the caret to the end of the post textbox (#5567)

webapp/components/file_upload.jsx

@@ -292,10 +292,12 @@ class FileUpload extends React.Component {
 
                 this.props.onUploadStart([clientId], channelId);
             }
-        }
 
+            if (numToUpload > 0) {
                 this.props.onFileUploadChange();
             }
+        }
+    }
 
     keyUpload(e) {
         if (Utils.cmdOrCtrlPressed(e) && e.keyCode === Constants.KeyCodes.U) {