installer: record the default choice for the Default Branch option

If the user wants to simply follow what Git wants to use as the default
branch name in freshly-initialized repositories, we used to record the
empty string.

Except we didn't.

Because InnoSetup's `SetPreviousData()` function special-cases the empty
string to mean "delete that key from the previous data instead of
recording a value" (even if the documentation does not spell that out:
https://jrsoftware.org/ishelp/index.php?topic=isxfunc_setpreviousdata).

Let's just use a single space character instead of the empty string
(which does not specify a valid branch name) to indicate that the user
did not want to override Git's default.

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

Author: dscho

installer/install.iss

@@ -1899,7 +1899,8 @@ begin
     // Restore the setting chosen during a previous install.
     Data:=ReplayChoice('Default Branch Option','');
     case Data of
-        '': RdbDefaultBranch[DB_Unspecified].Checked:=True;
+        '':  RdbDefaultBranch[DB_Unspecified].Checked:=True;
+        ' ': RdbDefaultBranch[DB_Unspecified].Checked:=True;
     else begin
         RdbDefaultBranch[DB_Manual].Checked:=True;
         EdtDefaultBranch.Text:=Data;
@@ -3162,7 +3163,7 @@ begin
     RecordChoice(PreviousDataKey,'Custom Editor Path',CustomEditorData);
 
     // Default Branch options.
-    Data:='';
+    Data:=' ';
     if RdbDefaultBranch[DB_Manual].Checked then
         Data:=EdtDefaultBranch.Text;
     RecordChoice(PreviousDataKey,'Default Branch Option',Data);