Fix regex for extracting the project title from a .sb file

src/containers/sb-file-uploader.jsx

@@ -80,8 +80,9 @@ class SBFileUploader extends React.Component {
     }
     getProjectTitleFromFilename (fileInputFilename) {
         if (!fileInputFilename) return '';
-        // only parse title from files like "filename.sb2" or "filename.sb3"
-        const matches = fileInputFilename.match(/^(.*)\.sb[23]$/);
+        // only parse title with valid scratch project extensions
+        // (.sb, .sb2, and .sb3)
+        const matches = fileInputFilename.match(/^(.*)\.sb[23]?$/);
         if (!matches) return '';
         return matches[1].substring(0, 100); // truncate project title to max 100 chars
     }