[fba-rio]

Fix float type mismatch in dot() comparison.

[jaime-jmebot]

Looks good — small and correct.

• dot() returns a float, so comparing against 0.0 instead of 0 removes the int→float implicit conversion, which stricter compilers (notably GLSL ES on mobile/WebGL) reject.
• The change now matches the non-multisample PostShadowFilter.frag, so both shadow-filter variants behave identically.
• The extra spacing/brace-indentation tidy-up is harmless and keeps the block consistent with the rest of the file.

Thanks for the fix!