RT3823: Improve the robustness of event logging

There are a couple of minor fixes here:

1) Handle the case when RegisterEventSource() fails (which it may for
various reasons) and do the work of logging the event only if it succeeds.

2) Handle the case when ReportEvent() fails and do our best in debug builds
to at least attempt somehow indicate that something has gone wrong. The
typical situation would be someone running tools like DbMon, DBWin32,
DebugView or just having the debugger attached. The intent is to make sure
that at least some data will be captured so that we can save hours and days
of debugging time.

3) Minor fix to change the MessageBox() flag to MB_ICONERROR. Though the
value of MB_ICONERROR is the same value as MB_ICONSTOP, the intent is
better conveyed by using MB_ICONERROR.

Testing performed:

1) Clean compilation for debug-VC-WIN32 and VC-WIN32.

2) Good test results (nmake -f ms\ntdll.mak test) for debug-VC-WIN32 and
VC-WIN32.

3) Stepped through relevant changes using WinDBG and exercised the impacted
code paths.
Signed-off-by: NRich Salz <rsalz@akamai.com>
Reviewed-by: NMatt Caswell <matt@openssl.org>

crypto/cryptlib.c

@@ -409,13 +409,29 @@ void OPENSSL_showfatal(const char *fmta, ...)
 # if defined(_WIN32_WINNT) && _WIN32_WINNT>=0x0333
     /* this -------------v--- guards NT-specific calls */
     if (check_winnt() && OPENSSL_isservice() > 0) {
-        HANDLE h = RegisterEventSource(0, _T("OPENSSL"));
-        const TCHAR *pmsg = buf;
-        ReportEvent(h, EVENTLOG_ERROR_TYPE, 0, 0, 0, 1, 0, &pmsg, 0);
-        DeregisterEventSource(h);
+        HANDLE hEventLog = RegisterEventSource(NULL, _T("OpenSSL"));
+
+        if (hEventLog != NULL) {
+            const TCHAR *pmsg = buf;
+
+            if (!ReportEvent(hEventLog, EVENTLOG_ERROR_TYPE, 0, 0, NULL,
+                             1, 0, &pmsg, NULL)) {
+#if defined(DEBUG)
+                /*
+                 * We are in a situation where we tried to report a critical
+                 * error and this failed for some reason. As a last resort,
+                 * in debug builds, send output to the debugger or any other
+                 * tool like DebugView which can monitor the output.
+                 */
+                OutputDebugString(pmsg);
+#endif
+            }
+
+            (void)DeregisterEventSource(hEventLog);
+        }
     } else
 # endif
-        MessageBox(NULL, buf, _T("OpenSSL: FATAL"), MB_OK | MB_ICONSTOP);
+        MessageBox(NULL, buf, _T("OpenSSL: FATAL"), MB_OK | MB_ICONERROR);
 }
 #else
 void OPENSSL_showfatal(const char *fmta, ...)