Fix NetApiBufferReallocate and add a few tests for the border cases

dlls/netapi32/apibuf.c

@@ -60,11 +60,17 @@ NET_API_STATUS WINAPI NetApiBufferReallocate(LPVOID OldBuffer, DWORD NewByteCoun
                                              LPVOID* NewBuffer)
 {
     TRACE("(%p, %ld, %p)\n", OldBuffer, NewByteCount, NewBuffer);
-    *NewBuffer = HeapReAlloc(GetProcessHeap(), 0, OldBuffer, NewByteCount);
-    if (*NewBuffer)
-        return NERR_Success;
-    else
-        return GetLastError();
+    if (NewByteCount) 
+    {
+	*NewBuffer = HeapReAlloc(GetProcessHeap(), 0, OldBuffer, NewByteCount);
+	return *NewBuffer ? NERR_Success : GetLastError();
+    } 
+    else 
+    {
+	if (!HeapFree(GetProcessHeap(), 0, OldBuffer)) return GetLastError();
+	*NewBuffer = 0;
+	return NERR_Success;
+    }
 }
 
 /************************************************************

dlls/netapi32/tests/apibuf.c

@@ -63,7 +63,14 @@ void run_apibuf_tests(void)
     ok(dwSize >= 0, "The size");
     ok(pNetApiBufferSize(NULL, &dwSize) == ERROR_INVALID_PARAMETER, "Error for NULL pointer");
 
-   /* 0-length buffer */
+    /* border reallocate cases */
+    ok(pNetApiBufferReallocate(0, 1500, (LPVOID *) &p) != NERR_Success, "(Re)allocated");
+    ok(p == NULL, "Some memory got allocated");
+    ok(pNetApiBufferAllocate(1024, (LPVOID *)&p) == NERR_Success, "Memory not reserved");
+    ok(pNetApiBufferReallocate(p, 0, (LPVOID *) &p) == NERR_Success, "Not freed");
+    ok(p == NULL, "Pointer not cleared");
+    
+    /* 0-length buffer */
     ok(pNetApiBufferAllocate(0, (LPVOID *)&p) == NERR_Success,
        "Reserved memory");
     ok(pNetApiBufferSize(p, &dwSize) == NERR_Success, "Got size");