Fix missing angle zerolization when 2d stabilization is disabled.

Not sure how it wasn't noticed for so long, probably check happens
in callee as well, but better be safe than sorry here.

source/blender/blenkernel/intern/tracking.c

@@ -3582,6 +3582,9 @@ ImBuf *BKE_tracking_stabilize_frame(MovieTracking *tracking, int framenr, ImBuf
 		if (scale)
 			*scale = 1.0f;
 
+		if (angle)
+			*angle = 0.0f;
+
 		return ibuf;
 	}