user: Set buffer to '\0' in GetKeyNameTextA too.

dlls/user/input.c

@@ -595,7 +595,10 @@ INT WINAPI GetKeyNameTextA(LONG lParam, LPSTR lpBuffer, INT nSize)
     INT ret;
 
     if (!GetKeyNameTextW(lParam, buf, 256))
+    {
+        lpBuffer[0] = 0;
         return 0;
+    }
     ret = WideCharToMultiByte(CP_ACP, 0, buf, -1, lpBuffer, nSize, NULL, NULL);
     if (!ret && nSize)
     {

dlls/user/tests/input.c

@@ -521,8 +521,22 @@ static void test_Input_blackbox(void)
     DestroyWindow(window);
 }
 
+static void test_keynames(void)
+{
+    int i, len;
+    char buff[256];
+
+    for (i = 0; i < 512; i++)
+    {
+        strcpy(buff, "----");
+        len = GetKeyNameTextA(i << 16, buff, sizeof(buff));
+        ok(len || !buff[0], "%d: Buffer is not zeroed\n", i);
+    }
+}
+
 START_TEST(input)
 {
     test_Input_whitebox();
     test_Input_blackbox();
+    test_keynames();
 }