Fixed other instances of the xrealloc(0) bug.

diff --git a/tools/winegcc/utils.c b/tools/winegcc/utils.c
index ee404d5..6d5d31e 100644
--- a/tools/winegcc/utils.c
+++ b/tools/winegcc/utils.c
@@ -60,8 +60,8 @@
 
 void *xrealloc(void* p, size_t size)
 {
-    void* p2;
-    if ((p2 = realloc (p, size)) == NULL)
+    void* p2 = realloc (p, size);
+    if (size && !p2)
 	error("Can not realloc %d bytes.", size);
 
     return p2;