dbghelp: Use dbgstr_a() in case pointer is NULL

[Andrew Talbot]

Offered in place of "dbghelp: Fix stabs_pts_read_type_def() for when typename
is NULL", after advice from Eric Pouech.

-- Andy.
---
Changelog:
    dbghelp: Use dbgstr_a() in case pointer is NULL.

diff --git a/dlls/dbghelp/stabs.c b/dlls/dbghelp/stabs.c
index d550633..9955b7e 100644
--- a/dlls/dbghelp/stabs.c
+++ b/dlls/dbghelp/stabs.c
@@ -1003,7 +1003,7 @@ static int stabs_pts_read_type_def(struct ParseTypedefData* ptd, const char* typ
 
     *stabs_find_ref(filenr1, subnr1) = *ret_dt = new_dt;
 
-    TRACE("Adding (%ld,%ld) %s\n", filenr1, subnr1, typename);
+    TRACE("Adding (%ld,%ld) %s\n", filenr1, subnr1, debugstr_a(typename));
 
     return 0;
 }