clRateMetalTable(): roundoff issue when checking for table overflow

[trquinn]

The checks for table overflow/underflow in clRateMetalTable() in cooling_metal.c and cooling_metal_H2.c have roundoff problems. E.g. if cl->z is greater than cl->MetalzMin by an amount that will be lost in roundoff when calculating "xz", there will be a table overflow. The "EPS" should be included in the if() test to fix this.