shader value validation (#20086)

Author: Mee-gu

tests/cpp-tests/Resources/Shaders/example_Flower.fsh

@@ -25,7 +25,10 @@ void main(void)
 	float h = 0.5+0.5*cos(12.0*a-w*7.0+r*8.0);
 	float d = 0.25+0.75*pow(h,1.0*r)*(0.7+0.3*w);
 
-	float col = u( d-r ) * sqrt(1.0-r/d)*r*2.5;
+	float rd = 1.0-r/d;
+	float col = 0.0;
+	if(rd > 0.0)
+	    col = u( d-r ) * sqrt(rd)*r*2.5;	
 	col *= 1.25+0.25*cos((12.0*a-w*7.0+r*8.0)/2.0);
 	col *= 1.0 - 0.35*(0.5+0.5*sin(r*30.0))*(0.5+0.5*cos(12.0*a-w*7.0+r*8.0));
 	gl_FragColor = vec4(