mshtml/tests: Remove an always true conditional subexpression (PVS-Studio)

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=11654

Your paranoid android.


=== wvistau64 (32 bit events) ===
events.c:939: Test failed: unexpected call img_onerror

=== w7u (32 bit events) ===
events.c:939: Test failed: unexpected call img_onerror
The test timed out