WebGLClipping: Set numIntersection to 0 in projectPlanes().

[ricardoreiter]

Fixed #18675.

When setState() gets called with a material that has no clipping planes and shadows are enabled, it will enter this line

three.js/src/renderers/webgl/WebGLClipping.js

Line 69 in f7dd2f0

projectPlanes( null );

Which resets the numPlanes but not the numIntersection which was dirty with old values from previous materials with clipping planes.

[mrdoob]

Thanks!