Possible nan in IVAS IGF decoder

In the function IGF_replaceTCXNoise_2_new (only used in IVAS) a possible nan value can occur. This function is called for every IGF tile with no or mid-whitening. If there is only one bin in the tile which is classified as noise and own_rand function happens to give back 0 for this one bin, then a division by FLT_MIN occurs which can result in nan.

This scenario is extremely rare but can destroy the whole frame if it does happen and should therefore be fixed.