Make WASMFS FS.createPath match the FS version behavior on EEXIST

If the file packager tries to add content to *an existing path* in the
filesystem (e.g., if the filesystem already has some directories, OPFS
content, loading multiple package, etc), the different behavior of
createPath causes an exception on WASMFS and no exception on JS FS.

src/lib/libwasmfs.js

@@ -111,7 +111,11 @@ FS.init();
         if (!wasmFSPreloadingFlushed) {
           wasmFSPreloadedDirs.push({parentPath: parent, childName: part});
         } else {
-          FS.mkdir(current);
+          try {
+            FS.mkdir(current);
+          } catch (e) {
+            if (e.errno != {{{ cDefs.EEXIST }}}) throw e;
+          }
         }
         parent = current;
       }

test/test_browser.py

@@ -1881,6 +1881,22 @@ def setup():
     shutil.copy(Path('sub/test.data'), '.')
     self.btest_exit('test_emscripten_async_load_script.c', args=['-sFORCE_FILESYSTEM'])
 
+  @also_with_wasmfs
+  def test_emscripten_overlapped_package(self):
+    def setup():
+      create_file('script1.js', '''
+        Module._set(456);
+      ''')
+      ensure_dir('sub')
+      create_file('sub/file1.txt', 'first')
+      create_file('sub/file2.txt', 'second')
+
+    setup()
+    self.run_process([FILE_PACKAGER, 'test.data', '--preload', 'sub/file1.txt@/target/file1.txt'], stdout=open('script2.js', 'w'))
+    self.run_process([FILE_PACKAGER, 'test2.data', '--preload', 'sub/file2.txt@/target/file2.txt'], stdout=open('script3.js', 'w'))
+    self.btest_exit('test_emscripten_overlapped_package.c', args=['-sFORCE_FILESYSTEM'])
+    self.clear()
+
   def test_emscripten_api_infloop(self):
     self.btest_exit('emscripten_api_browser_infloop.cpp', assert_returncode=7)
 

test/test_emscripten_overlapped_package.c

@@ -0,0 +1,66 @@
+// Copyright 2013 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#include <emscripten.h>
+
+int value = 0;
+
+EMSCRIPTEN_KEEPALIVE void set(int x) {
+  printf("set! %d\n", x);
+  value = x;
+}
+
+void load3() {
+  printf("load3\n");
+  char buffer[10];
+  memset(buffer, 0, 10);
+  FILE *f = fopen("/target/file1.txt", "r");
+  assert(f);
+  fread(buffer, 1, 5, f);
+  fclose(f);
+  assert(strcmp(buffer, "first") == 0);
+
+  memset(buffer, 0, 10);
+  f = fopen("/target/file2.txt", "r");
+  assert(f);
+  fread(buffer, 1, 6, f);
+  fclose(f);
+  assert(strcmp(buffer, "second") == 0);
+  exit(0);
+} 
+
+void error3() {
+  printf("fail3\n");
+}
+
+void error2() {
+  printf("fail2\n");
+}
+
+void load2() {
+  printf("load2\n");
+  emscripten_async_load_script("script3.js", load3, error3);
+}
+
+void load1() {
+  printf("load1\n");
+  assert(value == 456);
+
+  emscripten_async_load_script("script2.js", load2, error2);
+}
+
+void error1() {
+  printf("fail1\n");
+}
+
+int main() {
+  emscripten_async_load_script("script1.js", load1, error1);
+  return 99;
+}