OUString::matchIgnoreAsciiCase returns bool

Regression introduced with d2272426cc "Use some
more C++ in sal/osl/w32", found with loplugin:implicitboolconversion.

Change-Id: I5d929dd64bc02559318b8c89cb66bb0f5bba33f7
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/140072
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sal/osl/w32/file_url.cxx

@@ -581,7 +581,7 @@ oslFileError osl_getSystemPathFromFileURL_(const OUString& strURL, rtl_uString *
 
     SAL_WARN_IF(
         sUTF8.getLength() != strURL.getLength() &&
-        0 == strURL.matchIgnoreAsciiCase("file:\\")
+        strURL.matchIgnoreAsciiCase("file:\\")
         , "sal.osl"
         ,"osl_getSystemPathFromFileURL: \"" << strURL << "\" is not encoded !!!");