[bun:error] Fix exception

packages/bun-error/index.tsx

@@ -1390,6 +1390,7 @@ export function renderRuntimeError(error: Error) {
               remapped[1];
         }, console.error);
       } else {
+        if (!mappings) return null;
         var frame = exception.stack.frames[frameIndex];
         const { line, column_start } = frame.position;
         const remapped = remapPosition(mappings, line, column_start);

packages/bun-error/sourcemap.ts

@@ -281,7 +281,7 @@ export function fetchAllMappings(files, signal) {
 
   for (const [file, indices] of [...map.entries()]) {
     const mapped = fetchMappings(file, signal);
-    if (mapped.then) {
+    if (mapped?.then) {
       var resolvers = [];
       for (let i = 0; i < indices.length; i++) {
         results[indices[i]] = new Promise((resolve, reject) => {