util: Avoid possible error in virCommandMassClose

Avoid the chance that sysconf(_SC_OPEN_MAX) returns -1 and thus
would cause virBitmapNew would attempt to allocate a very large
bitmap.

Found by Coverity
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
ACKed-by: NPeter Krempa <pkrempa@redhat.com>

src/util/vircommand.c

@@ -487,6 +487,11 @@ virCommandMassClose(virCommandPtr cmd,
      * Therefore we can safely allocate memory here (and transitively call
      * opendir/readdir) without a deadlock. */
 
+    if (openmax < 0) {
+        virReportSystemError(errno, "%s", _("sysconf(_SC_OPEN_MAX) failed"));
+        return -1;
+    }
+
     if (!(fds = virBitmapNew(openmax)))
         return -1;