hwaccel_vdpau.h: add config.h include guard

allows build outside of UG/when config.h not generated

Also helps when building tools/convert even when config.h is generated,
VDPAU enabled but FFmpeg headers in non-standard path (that is obtained
by pkgconf for UG but not for the tool).

Author: MartinPulec

src/hwaccel_vdpau.h

@@ -45,7 +45,9 @@
 #ifndef HWACCEL_VDPAU_H
 #define HWACCEL_VDPAU_H
 
+#ifdef HAVE_CONFIG_H
 #include "config.h"         // for HWACC_VDPAU
+#endif
 
 #ifdef HWACC_VDPAU