winebuild: Don't segfault when running without arguments

[André Hentschel]

Before:
$ winebuild 
Segmentation fault

---
 tools/winebuild/main.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/winebuild/main.c b/tools/winebuild/main.c
index f6c04fd..ba8a629 100644
--- a/tools/winebuild/main.c
+++ b/tools/winebuild/main.c
@@ -142,13 +142,13 @@ static void set_dll_file_name( const char *name, DLLSPEC *spec )
 /* set the dll name from the file name */
 static void init_dll_name( DLLSPEC *spec )
 {
-    if (!spec->file_name)
+    if (!spec->file_name && output_file_name)
     {
         char *p;
         spec->file_name = xstrdup( output_file_name );
         if ((p = strrchr( spec->file_name, '.' ))) *p = 0;
     }
-    if (!spec->dll_name)  /* set default name from file name */
+    if (!spec->dll_name && spec->dll_name)  /* set default name from file name */
     {
         char *p;
         spec->dll_name = xstrdup( spec->file_name );
-- 

Best Regards, André Hentschel