[perl #58438] [PATCH] nci can't pass NULL string arguments

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I was doing a simple test of NCI calls with the xlib function
XDisplayName, and found that nci can't handle a NULL string argument.
Passing a NULL Parrot String segfaults.

The attached patch passes a NULL char * when a NULL Parrot String is
used. Don't know if this is the desired behaviour, I expect comments.

-- 
Salu2

Index: tools/build/nativecall.pl
===================================================================
--- tools/build/nativecall.pl   (revision 30618)
+++ tools/build/nativecall.pl   (working copy)
@@ -505,8 +505,8 @@
     /t/ && do {
         push @{$temps_ref}, "char *t_$temp_num;";
         push @{$extra_preamble_ref},
-            "t_$temp_num = string_to_cstring(interp, GET_NCI_S($reg_num));";
-        push @{$extra_postamble_ref}, "string_cstring_free(t_$temp_num);";
+            "{STRING * s= GET_NCI_S($reg_num); t_$temp_num = s ? 
string_to_cstring(interp, s) : (char *) NULL;}";
+        push @{$extra_postamble_ref}, "do { if (t_$temp_num) 
string_cstring_free(t_$temp_num); } while (0);";
         return "t_$temp_num";
     };
     /b/ && do {