user32: Add missing NULL check.

[Grazvydas Ignotas]

---
 dlls/user32/combo.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/dlls/user32/combo.c b/dlls/user32/combo.c
index 9c22df6..4551254 100644
--- a/dlls/user32/combo.c
+++ b/dlls/user32/combo.c
@@ -1800,7 +1800,7 @@ static char *strdupA(LPCSTR str)
 
     len = strlen(str);
     ret = HeapAlloc(GetProcessHeap(), 0, len + 1);
-    memcpy(ret, str, len + 1);
+    if (ret) memcpy(ret, str, len + 1);
     return ret;
 }
 
-- 
1.7.0.4