installer: actually record user's Git Credential Manager choice

We diligently tried to use the previous choice whether to enable the Git
Credential Manager or not, but we never recorded that choice.

Until now.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

installer/install.iss

@@ -1931,6 +1931,11 @@ begin
     end;
     RecordChoice(PreviousDataKey,'Performance Tweaks FSCache',Data);
     Data:='Disabled';
+    if RdbExtraOptions[GP_GCM].Checked then begin
+        Data:='Enabled';
+    end;
+    RecordChoice(PreviousDataKey,'Use Credential Manager',Data);
+    Data:='Disabled';
     if RdbExtraOptions[GP_Symlinks].Checked then begin
         Data:='Enabled';
     end;