[WasmFS] Fix asan.test_fs_js_api_wasmfs (#23898)

Author: sbc100

.circleci/config.yml

@@ -537,6 +537,7 @@ jobs:
             asan.test_asyncify_longjmp
             asan.test_pthread_run_on_main_thread
             asan.test_minimal_runtime_global_initializer
+            asan.test_fs_js_api_wasmfs
             lsan.test_dylink_dso_needed
             lsan.test_stdio_locking
             lsan.test_dlfcn_basic

src/lib/libwasmfs.js

@@ -195,13 +195,12 @@ addToLibrary({
       } else {
         bytesRead = __wasmfs_read(stream.fd, dataBuffer, length);
       }
-      bytesRead = FS.handleError(bytesRead);
-
-      for (var i = 0; i < length; i++) {
+      for (var i = 0; i < bytesRead; i++) {
         buffer[offset + i] = {{{ makeGetValue('dataBuffer', 'i', 'i8')}}}
       }
 
       _free(dataBuffer);
+      bytesRead = FS.handleError(bytesRead);
       return bytesRead;
     },
     // Note that canOwn is an optimization that we ignore for now in WasmFS.
@@ -219,8 +218,8 @@ addToLibrary({
       } else {
         bytesRead = __wasmfs_write(stream.fd, dataBuffer, length);
       }
-      bytesRead = FS.handleError(bytesRead);
       _free(dataBuffer);
+      bytesRead = FS.handleError(bytesRead);
 
       return bytesRead;
     },