[colr] Ensure enough bytes for PaintColrLayers

* src/sfnt/ttcolr.c (read_paint): check that there are five additional
bytes to be read when reading PaintColrLayers.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=66566

src/sfnt/ttcolr.c

@@ -661,6 +661,7 @@
       FT_UInt32  first_layer_index;
 
 
+      ENSURE_READ_BYTES( 5 );
       num_layers = FT_NEXT_BYTE( p );
       if ( num_layers > colr->num_layers_v1 )
         return 0;