vim: Let ninja-build.vim detect Release correctly if out/Debug/protoc doesn't exist at all.

tools/vim/ninja-build.vim

Index: tools/vim/ninja-build.vim
diff --git a/tools/vim/ninja-build.vim b/tools/vim/ninja-build.vim
index a8822231ad472b33d303fa2ab69c4f285ffa0e44..e753b18be5036c2fd69cfa8a592533704cd6ac4b 100644
--- a/tools/vim/ninja-build.vim
+++ b/tools/vim/ninja-build.vim
@@ -43,10 +43,13 @@ def guess_configuration():
   def is_release_15s_newer(test_path):
     try:
       debug_mtime = os.path.getmtime(os.path.join(root, 'Debug', test_path))
+    except os.error:
+      debug_mtime = 0
+    try:
       rel_mtime = os.path.getmtime(os.path.join(root, 'Release',  test_path))
-      return rel_mtime - debug_mtime >= 15
     except os.error:
-      return False
+      rel_mtime = 0
+    return rel_mtime - debug_mtime >= 15
   configuration = 'Debug'
   if is_release_15s_newer('build.ninja') or is_release_15s_newer('protoc'):
     configuration = 'Release'