conf: Remove ATTRIBUTE_NONNULL for virDomainQemuMonitorEventNew

Commit 17561eb3 modified the logic to check "if (!event)" for an
attribute that was not supposed to be passed as NULL.  This causes
the static checker/Coverity build to fail. Since the check is made,
alter the header.

Also add an error message since returning -1 without some sort of
error message as previously would have happened with the failed
VIR_STRDUP so that the eventual error doesn't get the default
for some reason message.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

src/conf/domain_event.c

@@ -1935,8 +1935,12 @@ virDomainQemuMonitorEventNew(int id,
         return NULL;
 
     /* event is mandatory, details are optional */
-    if (!event)
+    if (!event) {
+        virReportError(VIR_ERR_INVALID_ARG,
+                       _("unexpected event=NULL name=%s uuid=%s details=%s"),
+                       name, uuidstr, NULLSTR(details));
         goto error;
+    }
 
     ev->event = g_strdup(event);
     ev->seconds = seconds;

src/conf/domain_event.h

@@ -321,4 +321,4 @@ virDomainQemuMonitorEventNew(int id,
                              long long seconds,
                              unsigned int micros,
                              const char *details)
-    ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3) ATTRIBUTE_NONNULL(4);
+    ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3);