[pshinter] Fully initialize globals->blues.

These defaults may be overriden later by psh_blues_scale_zones which is conditionally called from psh_globals_set_scale.

• src/pshinter/pshglob.c (psh_globals_new): initialize blues->blue_threshold and blues->no_overshoots.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=43701