Remove a redundant call to GetRadioButtonAppStream().

Instead of calling GetRadioButtonAppStream() twice in a row, save and
reuse the result from the first call.

Change-Id: Id9b849e8cdc942b332cbb6ca59ed2800e245a3cd
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/66392
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

fpdfsdk/cpdfsdk_appstream.cpp

diff --git a/fpdfsdk/cpdfsdk_appstream.cpp b/fpdfsdk/cpdfsdk_appstream.cpp
index 8157314..e451977 100644
--- a/fpdfsdk/cpdfsdk_appstream.cpp
+++ b/fpdfsdk/cpdfsdk_appstream.cpp
@@ -1543,8 +1543,9 @@
 
   ByteString csAP_D_OFF = csAP_D_ON;
 
-  csAP_N_ON += GetRadioButtonAppStream(rcClient, nStyle, crText);
-  csAP_D_ON += GetRadioButtonAppStream(rcClient, nStyle, crText);
+  ByteString app_stream = GetRadioButtonAppStream(rcClient, nStyle, crText);
+  csAP_N_ON += app_stream;
+  csAP_D_ON += app_stream;
 
   Write("N", csAP_N_ON, pControl->GetCheckedAPState());
   Write("N", csAP_N_OFF, "Off");