DRW: Fix stencil being modified by passes that are read only

This is because even if the glStencilMask is 0x00 the GL_DECR_WRAP and
GL_INCR_WRAP states still works and will modify the stencil.

Fix T73046 Overlapping parts of wireframes don't render at all in workench
with shadows turned on.

source/blender/draw/intern/draw_manager_exec.c

@@ -129,6 +129,7 @@ void drw_state_set(DRWState state)
       }
       else {
         glStencilMask(0x00);
+        glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
       }
     }
   }