Fix FS forceLoadFile() function (#25004)

Fixes `strict_js.test_files` and other `strict_js` suite runs.

Author: juj

src/lib/libfs.js

@@ -1710,8 +1710,10 @@ FS.staticInit();`;
       } else { // Command-line.
         try {
           obj.contents = readBinary(obj.url);
-          obj.usedBytes = obj.contents.length;
         } catch (e) {
+ #if FS_DEBUG
+          dbg(`forceLoadFile exception: ${e}`);
+ #endif
           throw new FS.ErrnoError({{{ cDefs.EIO }}});
         }
       }

test/code_size/test_codesize_file_preload.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 22699,
-  "a.out.js.gz": 9379,
+  "a.out.js": 22684,
+  "a.out.js.gz": 9375,
   "a.out.nodebug.wasm": 1733,
   "a.out.nodebug.wasm.gz": 980,
-  "total": 24432,
-  "total_gz": 10359,
+  "total": 24417,
+  "total_gz": 10355,
   "sent": [
     "a (fd_write)"
   ],

test/other/codesize/test_codesize_file_preload.expected.js

@@ -2804,7 +2804,6 @@ var FS = {
       // Command-line.
       try {
         obj.contents = readBinary(obj.url);
-        obj.usedBytes = obj.contents.length;
       } catch (e) {
         throw new FS.ErrnoError(29);
       }