windows: Fix an infinite loop in uv_spawn

The PATH-parsing code for windows erroneously contained an infinite
loop when the PATH started with a leading semicolon. Each iteration of
the loop usually bumped over the separator, but if the first character
was a semicolon then it would never skip it, causing the infinite
loop.

Closes #909

src/win/process.c

@@ -378,7 +378,7 @@ static WCHAR* search_path(const WCHAR *file,
       }
 
       /* Skip the separator that dir_end now points to */
-      if (dir_end != path) {
+      if (dir_end != path || *path == L';') {
         dir_end++;
       }
 

test/test-list.h

@@ -244,6 +244,7 @@ TEST_DECLARE   (environment_creation)
 TEST_DECLARE   (listen_with_simultaneous_accepts)
 TEST_DECLARE   (listen_no_simultaneous_accepts)
 TEST_DECLARE   (fs_stat_root)
+TEST_DECLARE   (spawn_with_an_odd_path)
 #else
 TEST_DECLARE   (emfile)
 TEST_DECLARE   (close_fd)
@@ -500,6 +501,7 @@ TASK_LIST_START
   TEST_ENTRY  (listen_with_simultaneous_accepts)
   TEST_ENTRY  (listen_no_simultaneous_accepts)
   TEST_ENTRY  (fs_stat_root)
+  TEST_ENTRY  (spawn_with_an_odd_path)
 #else
   TEST_ENTRY  (emfile)
   TEST_ENTRY  (close_fd)

test/test-spawn.c

@@ -935,6 +935,28 @@ TEST_IMPL(environment_creation) {
 
   return 0;
 }
+
+// Regression test for issue #909
+TEST_IMPL(spawn_with_an_odd_path) {
+  int r;
+
+  char newpath[2048];
+  char *path = getenv("PATH");
+  ASSERT(path != NULL);
+  snprintf(newpath, 2048, ";.;%s", path);
+  SetEnvironmentVariable("PATH", path);
+
+  init_process_options("", exit_cb);
+  options.file = options.args[0] = "program-that-had-better-not-exist";
+  r = uv_spawn(uv_default_loop(), &process, &options);
+  ASSERT(r == UV_ENOENT || r == UV_EACCES);
+  ASSERT(0 == uv_is_active((uv_handle_t*) &process));
+  uv_close((uv_handle_t*) &process, NULL);
+  ASSERT(0 == uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}
 #endif
 
 #ifndef _WIN32