Fix an issue that no response from the call back function of FFI_GetLanguage()

fpdfsdk/src/javascript/app.cpp

Index: fpdfsdk/src/javascript/app.cpp
diff --git a/fpdfsdk/src/javascript/app.cpp b/fpdfsdk/src/javascript/app.cpp
index d18e0322abff79c17035657eb85f9a354cc11913..869a478387cda63868fa6e7dc15302fb82ab9b27 100644
--- a/fpdfsdk/src/javascript/app.cpp
+++ b/fpdfsdk/src/javascript/app.cpp
@@ -228,12 +228,19 @@ FX_BOOL app::platform(IJS_Context* cc,
 FX_BOOL app::language(IJS_Context* cc,
                       CJS_PropValue& vp,
                       CFX_WideString& sError) {
-  if (vp.IsGetting()) {
+  if (!vp.IsGetting())
+    return FALSE;
+  CPDFDoc_Environment* pEnv =
+      static_cast<CJS_Context*>(cc)->GetJSRuntime()->GetReaderApp();
+  if (!pEnv)
+    return FALSE;
+  CFX_WideString language = pEnv->FFI_GetLanguage();
+  if (language.IsEmpty())
     vp << JS_STR_LANGUANGE;
-    return TRUE;
-  }
+  else
+    vp << language;
 
-  return FALSE;
+  return TRUE;
 }
 
 // creates a new fdf object that contains no data